A/N: I have actually done this. And my coworkers whined at me for it looking dirty, so I went with it.
Disclaimer: I wish I owned cool stuff like this. Uhhh, I own a water bottle?
The second time, Steve walked in to the gym to find Natasha and Tony sparring in the boxing ring while Clint leaned against the ropes, complaining about how boring they were to watch.
"You both suck," Clint said. "Nobody's even bleeding yet."
Natasha put a hand on her hip and ducked one of Tony's punches. "I can make you bleed if you'd like, Clint."
"No, thank you," Clint said quickly.
"Then, shut up."
Steve chuckled and headed over to the punching bag. It was just close enough that he could still watch the sparring match. Natasha was winning, of course. She always won. But after several months of practice, Tony was getting better. And that was the important thing.
It was good to see Tony circling around Natasha, his eyes dark with intensity and sweat dripping down his body, plastering his shirt against his-
Well, it was good to see Tony taking sparring seriously, anyway.
After another fifteen minutes of basically dancing around each other, Natasha called for a break.
"Make yourself useful, Barton, and get me a water," Tony said.
Clint flipped him off, but he grabbed a water bottle out of the cooler and tossed it to Tony.
Tony twisted the cap partly off the bottle with his teeth and then pushed his mouth down over the bottle's neck. Now, with his hands free, Tony tapped at his tablet, bringing up footage of his match with Natasha so he could analyze it for next time.
"You weirdo," Clint said. "You can't drink it like that."
"Just watch me," Tony mumbled around the bottle. He curled one hand around the bottle and drank deeply. Steve could see the effort it took for Tony to get even the smallest sip. He hollowed his cheeks as he sucked vigorously. Still, Tony was definitely getting water out of it. He could see Tony's throat work as he swallowed.
"Hey, Steve," Natasha called. "Steve."
He blinked rapidly, realizing he had just been staring at Tony for the past five minutes. "Sorry," he said. "I've got a lot on my mind."
Natasha jerked a thumb towards Tony. "You want to go a round with him?" she asked. "Maybe teach him some of your moves?"
Of course he did. It was an excuse to put his hands on Tony, have him pinned beneath him, squirming and-
But no, it would be a bad idea. A very bad idea.
"You two go ahead," he said. "I'm done here."
Natasha raised an eyebrow. "But you just got here."
Tony tilted his head back and shook out the last drops of water onto his tongue.
Steve suppressed a shudder. "I'm going to go for a run instead."