Disclaimer: I do NOT own ATLA, the characters, or the plot (I only extended it by a bit). I was inspired by ~GreenifyMe 's drawing.

Katara'a POV

We had been traveling for hours through the sticky, hot summer weather when Aang finally decided that we needed to settle down for the night. The sun was high in the sky and the heat crashed over me, stifling me with its unbearable heat. Considering I was from the water nation, where it has constant snow year round, it was making me feel as if I were on fire myself. Overall, a highly unpleasant experience. I was already counting down the seconds till the cool night brought salvation from this torture.
"Ugh," I groaned, "its soooo hot today." I wiped the sweat from my forehead. I grabbed. My water pouch from the sash around my waist and opened it to drink tipping it almost completely vertical to capture the maximum amount of water. I only got one drop of from my water pouch, and frankly that would not be enough for the fiery thirst burning my throat and I wasn't about to use the water I used for healing to quench my thirst. So instead of going longer with a parched throat and a dry mouth, I did what any smart person would do: I started looking for my lovably idiotic brother's bag. I turned around and saw Sokka's bag sitting leaned up against a huge tree. I ignored the "Sokka's stuff, do NOT touch" sign and started shifting through his things. I dug through the pack and found the water sack buried under a mess of clothing. I made a note to myself that I would scold him for packing his things so messily. I would only condone this messy packing if there was an invasion and we only had time to throw things into bags.
I took the almost completely filled water pouch out of his bag, and mumbled to myself, "Sorry Sokka, but I'm borrowing some water". I took a deep, long drink from the pouch. There was something off about the drink, but I just couldn't seem to put my finger on it. I gradually came to the realization that it had a strange taste to it. Not water, I thought, defiantly not water. The drink was too sweet to be water, but it was certainly helping my thirst. I knew I had tasted this somewhere else but I couldn't think of where it had been or what the drink was. Then I started feeling different…It was too bitter to be water and the combination of sweet and bitter brought me to a horrible realization.
I realized that what I was drinking was the farthest thing from water, more like alcohol but even stronger; I was drinking cactus juice. Of all things there were to drink, Sokka had grabbed cactus juice. Humiliation nation here I come.

1 Hour later:

Sokka's POV

I was thirsty. And hungry. Yes, mainly hungry. I thought of the food and drinks I had stored in my stuff, and I walked toward it. I thought of the nuts, the berries, the meat... As I got closer to my bag I felt the gnawing worry that warned me that something was very wrong. There was something wrong with my pack, but I couldn't place what it was. As I came closer I saw that it was open. I frowned. I didn't remember opening it since I packed it. Okay, I had, but it was only when I was digging out some food. I opened it and did a quick check that everything was there. I had everything, but my favored drink. I stared in shock that the drink was gone where as everything else was there. I looked around me in alarm. Where was everybody?
I heard a sound then; a rustling and a drunken giggle. I whipped toward it and saw something. I walked closer, and I saw legs, and a splotch of blue clothing.
"Uh, hey…Katara…?" I asked.
I heard her saying something as I got closer, and then I heard a second voice. I saw more than two legs. The legs were to close for my liking. They were especially too close when my sister's blue legging clad legs were intertwined with legs that were clad in red and clearly male. As I turned past the tree I saw something I really wished I hadn't seen. I don't think any older brother wanted to see his baby sister in this kind of position. I was seeing red and it was more than just the red clothes.
Katara was all but laying on Zuko! She was holding a pouch, and I was ninety-nine point nine percent sure it was the drink I had stored. She had drunk my cactus juice. Her faced was flushed, and I hate to admit it, I really did, but she was speaking a tad too breathy and seductively to Zuko for my taste. I almost felt sorry for the flushed cheeked Fire Prince.
That all went out the window when I heard the conversation continue.
"Come on, Zuko, try it. It's gooood." She said just inches from his face.
Zuko saw me and started calling out to me.
"S-S-Sokka…help me." He tried to shout at me. It came out more like a desperate squeak and I have to admit that I had a sudden urge to laugh when I heard it.

Zuko's POV

This was too much, waaaayyyyy too much. She was practically laying on me and I couldn't bring myself to push her off of me. I'm a guy, I don't ogle the fairer sex like they were pieces of meat, but I was still a guy and I still had certain…reactions to women laying on me; especially when they were as gorgeous as the one currently on top of me. Her chestnut hair flowed down her back and spilled over her shoulders. Her face was flushed in a way too appealing to withstand. Her delicate looking hand clamped over my arm and still I would not, could not, push her away for the life of me. She held a bottle close to my face, but I didn't even glance at it. Her face was too close to mine to even have a thought other than her.
I was enjoying this too much for my own good. It was getting really hard to resist what my body was screeching at me to do. It was getting to be too much for me to handle. Her presence it's self was over whelming. The scent of her hair was like the smell of spring, I noted, but that thought flew from my head as she inched closer to me yet. As she did this though, I vaguely noticed a shadow moving in the trees. My eyes, of their own accord, flickered to see what caused the sudden movement. What I saw caused my blood to run cold.
It was Sokka. A shocked look plastered to his face; his face flushed either with embarrassment at seeing the awkward position that Katara and I were in and fury for us being in the position. From anger at the position Katara and I were in or embarrassment from walking in on this I was not positive about which was the more dominate emotion.
"S-S-Sokka…help me." I begged in a squeak that tried to be a shout. He looked like he both pitied me for being unable to move her and wanted to kill me for her being on top of me. I certainly hope it was pity that I couldn't do anything to get his sister off me without hurting her and me dying from Sokka seeing me possibly hurting her. I wished this would either get over now, or last forever.

What really didn't help me was Katara. While I had been focused on Sokka she had inched even closer to me. Our chests were pressed so tightly together I doubt a leaf would have not been squashed. It only got worse, or better to my hormone driven side, when she pressed her lips to mine in a heated kiss fueled by pure, unadulterated passion. I'd be lying if I said I didn't freeze up for a moment before kissing her back; I was so luck Sokka had already left or he would've had my head on a spear and certain…equipment of mine removed and feed to bears.
I silently sent my thanks to the Gods for small mercies and the wonderful creation called cactus juice.