It all started with an casual and perfectly harmless compliment.

Steve had been in the gym, laying into another punching bag like it had slept with his sister when Tony had wandered in. He'd been on his way to the bridge when his Steve-y Senses started tingling, and he'd understandably made a detour. Next to a couple minutes watching Steve tenderize inanimate objects in a tight shirt and sweatpants that he somehow wore more provocatively than most people wore expensive lingerie—

Make that all people.

—Fury could wait.

Slipping in, he leaned back against the wall by the doorway and contented himself to enjoy the view.

He'd made it all of about three seconds before shooting his mouth off.

"Nice ass, Cap'n," he said, loud enough that he was sure Steve (and Clint, lifting weights in the corner) would hear. Did the buns of steel come standard with the superpowers, or was it an add-on package?"

The unintentional double-entendre made him smirk, a smirk which promptly grew as Steve tensed and threw a punch so hard it sent the punching bag sailing across the room into the far wall, knocking over a weight bench in the process.

When Steve turned around, his face was red from chin to the very tips of his ears. Tony knew some of it was probably from the exercise, but he was gonna take credit for most of it.

It amused him to no end how, after fighting Nazis and aliens and various psycho- and sociopathic evil-doers, Steve still managed to get so flustered over the little things. It was probably best the bad guys hadn't figured it out; they were so busy trying out their death rays and goons and all that other nonsense, ignorant to the one true weakness of Captain America:

Shameless flirting.

As endearing and amusing as the near-nuclear blushing and the awkward stammering were, though, that wasn't why he did it. He flirted because he genuinely liked the guy – no, more than liked him – and he was…testing the waters. Steve was always so uptight, and he looked out for everyone. It was hard to tell where he stood on anything, or even how he'd act on where he stood.

In simple terms, Steve was probably one of the bravest and most intelligent men Tony knew (not that he would tell him that; at least not directly), but in the realm of social interaction…

He was hopeless.

Cue Tony's little experiment. He needed to see how far he could go, where Steve would draw the line. He needed to be able to find the line to toe it, toe it to cross it, and cross it to redraw it so that Steve could finally stop holding back and act on the feelings that Tony was, if not certain, then pretty damn confident he had.

"What?" Steve said. It looked like he couldn't quite decide whether he wanted to be more indignant or mortified, though the former started nosing ahead when he glanced over at Clint.

The archer promptly went back to lifting, pretending not to be paying attention to the other occupants of the room.

He wasn't going to be winning any Oscars for the performance.

Doing his best to mask his amusement, Tony squared up his shoulders, feigning innocence. "Your ass," he said, as casually as if he were remarking on the weather. "It's very nice. You sure you don't do pilates?"

Steve's expression shifted from one of indignation to one of discomfort, and even a little bit of irritation. His jaw worked, and his eyes hardened just a bit.

Tony considered it progress.

"That's inappropriate," he said. There was a warning in his tone. Don't go there, it said.

So, naturally, Tony went there.

"Inappropriate? How is that inappropriate? I compliment Natasha's ass on a regular basis, and I'm not even the worst offender. I don't generally hear you piping up when half the Y chromosomes in the room are ogling her…unless—" he feigned surprise, "my, my, aren't we the chivalrous one? And by chivalrous, of course, I mean misogynistic chauvinist. Next you'll be telling us to keep her in the kitchen where she—"

"It has nothing to do with her being a dame—" he realized his mistake and practically grimaced before taking what Tony guessed was meant to be a calming breath, "—with her being a woman."

"So, it's more about you being a man."

He didn't phrase it like a question, rather like a psychologist would state a conclusion to an unruly patient. Knowingly, patronizingly.

If Steve wasn't flustered before, he certainly was now. His face was still red, and the vein at the base of his neck thrummed a quick rhythm that Tony could see under his sweat-dampened skin. "Tony, I don't know what you're—"

"Or maybe it's about me being a man. Because I've seen plenty of 'dames' checking out the junk in the trunk without a single complaint. Either way, that's sexist of you, and I'm disappointed. I thought you of all people would be able to rise above gender profiling, and—"

—And Steve was grabbing his stuff. And walking towards – no, scratch that, past – Tony without another word.

"—and this is going to be a little more tricky than I thought," he said once Steve was gone. Sighing, he sat down on the nearest weight bench. He ran a hand through his hair.

When he looked up again, Clint was watching him from his bench, the weights apparently long-forgotten.

"He's going to beat the shit out of you one of these days," Clint said offhandedly. "And you're gonna deserve every damn bit of it."

"I'd ask you to at least act concerned, but I've seen your acting, and frankly, I'm wondering how you lived so long as a spy if you can't—"

Clint let out a bark of a laugh. "Yeah, 'cause that's what the problem is here. My shitty acting. It has nothing to do with you being too chicken shit to man up and just ask the guy out."

"Who said I wanted to ask him out?"

The pointed look Clint shot his way, as if to say "how stupid do you think I am," was all the response necessary.

"No appreciation for subtlety, either," Tony said almost admonishingly, rising from the bench. "You, sir, are a pimple on the collective face of spies everywhere."

"And you're a snip to the collective balls of men everywhere. Just grow a pair and stop antagonizing the poor bastard, or else."

Tony raised an eyebrow. "At the risk of setting myself up for a cliché, or else what?"

"Or else I'll beat the shit out of you and save Steve the trouble."

And with that, ultimatum successfully delivered, Clint laid back on the bench and grabbed the bar.

"I'll just go propose to him then, shall I?" Tony said, and under his breath, he added, "I think all your time on rooftops has your brain starved for oxygen."

Though he wasn't entirely sure how Clint managed to free up both his middle fingers from the bar, Tony had to admit he was impressed.

Still, seething exeunt aside, this had been a success. He'd found the line in the sand.

Now he just had to figure out how to go about redrawing it.