Reread the chapter called Old Man II.
Caught I
"Mmm. Stop it." Toph giggled.
"Make me." Aang teased her as he tickled her side. They were just hanging out again, on Aang's dusty old couch, and Aang got bored.
"No, seriously. Off!" Toph pushed him gently. 'Gently' meant that she was only pretending to get him to stop. Aang had learned that, so he kept going. "Aang!" She squealed gently, but silenced herself when she realized that her feminine was taking over.
"Ha! I made you…" Aang was about to say 'giggle like a little girl', but Toph put her hand over his mouth and all that came was "…mmhm mh m mmhhm hmh."
"Yeah, I know you did. Don't be so proud of yourself twinkle toes. "
Aang grabbed her wrist and pulled her hand off, then immediately began to tickle her again.
"AAhh! Stop it, stop it, no, no, no. I'm serious! Stooaahahaoop!" Toph begged but didn't fight back. She fell backwards, pulling Aang on top of her.
"What is going on here?" Gyatso's voice came out of nowhere. Toph and Aang froze. They looked up and Aang's guardian was standing over them, arriving home earlier than usual.
"Um…" Aang's tongue swelled up in his mouth and he could speak. Both of their faces became fire red.
"I think I need to leave." Toph whispered to Aang, embarrassed.
"Yeah…okay." Aang said as he got off her. Toph covered her red face as she walked out of Aang's door without saying goodbye to either of them.
Aang sat up straight, placing his hands on his knees. He felt ashamed.
Gyatso didn't seem mad. He stared at his son with a plain face for a few seconds without saying a word. He pulled up a chair in front of him and sighed.
"…Gyatso, I…" Aang started, but Gyatso held up his open palm, signaling 'silence'.
"How long has this been going on for?" He asked without sounding angry.
"Um…well, sir…" Aang only called Gyatso 'sir' when he was nervous. "…since summer. Since we got back from…" Gyatso put his palm up again.
"Hmm." Gyatso rubbed his chin. "Aang, I've tried to teach you through example and through kind words. And I have been very patient with you, especially with the …ahem changes you've been going through.."
"Gyatso…I didn't mean to. I mean…I love her. We won't do anything here again, okay. I promise. I'll be polite, and respectful and…"
"Aang, Aang, slow down. I'm disappointed only because you didn't tell me about it." He leaned forward. "I have actually…known that you two were…more than friends for a while now."
"You did?" Aang's eyebrows jumped.
"On, come on now Aang, how could I not know?" Aang blushed. "I just want you to remember that I totally called that." Gyatso laughed and patted his young man on his shoulder. Aang smiled a bit, then Gyatso said, "But don't do that on my couch again."
"Yes sir!" Aang tensed up again. He could not believe what had happened.