Steve collided with Tony when the shorter man stopped abruptly in front of him.
About to cuff him across the back of the head, Steve paused, watching as the color receded from Tony's face and a cold sweat bead across his forehead.
Tony was rigid, breathing shallowly, eyes locked dead ahead of him. Steve backed up, and looked where Tony was so fixated.
Nothing seemed strange, a group of college kids were taking 'selfies', an older couple were strolling hand in hand laughing fondly as their dog trotted ahead of them. A few pigeons.
"Tony?" No response other than a tight shudder through the scientist's body and the immediate pickup of their conversation from where Tony had stopped.
Steve cast another glance into the crowd that had so transfixed Tony, then trotted to catch up to the fast talking man.
It happened again a few days later.
Abrupt, dead silence. Steve was almost certain that Tony had bitten his tongue this time. Steve parked himself in front of Tony and scanned his friend's line of sight.
Two girls giggling and taking photos on their cell phones, someone walking with a large package. A few marines in their combat boots and fatigued pants posing with their friends in front of a poorly worded advertisement.
This time Steve felt a small grip of worry seize him as he watched Tony's pulse thunder in his temple. Tony's hands shook, they were clenched so tight at his sides.
Instead of speaking, Steve positioned his face in front of Tony's, and blocked his view. Tony started, blinking away the beginnings of tears, and flashed a too bright, fake grin at Steve before practically running to his car.
They were with the whole team at Coney Island for Steve's birthday. Clint and Natasha joined Tony in his apparent quest to ask, every six feet, if Steve had "been beat up here too,"
After he'd affectionately growled "No, but if you ask again, YOU will be!" They'd switched to asking how much the boardwalk had changed, and if he recognized it in color.
Hilarious.
Bruce came hurrying over with cotton candy, and excitedly pointed to where there was a photo op set up-featuring the Avengers.
Little kids and adults alike were posing like action movie extras in front of a huge dynamic mural of the whole team.
Everyone agreed that this was the single best thing, and they hurried over, delighting the people gathered there.
As they positioned themselves in front of themselves, the crowd hooted and laughed.
Natasha and Clint adopted synchronized positions, Bruce contorted his face into the most absurd 'angry' expression he could, and Thor... well, Thor posed like he was in a L'Oreal commercial.
Tony was just pulling his shirt collar down and turning toward him when Steve cocked his hip and flashed up a 'Peace' Sign.
Tony's smile withed, his breath caught in his throat and Steve saw his pupils constrict into pinpricks.
He had just enough time for each incident to flash before his eyes. The college kids with their arms outstretched, fingers spread into jubilant V's. The marines throwing up their hands in front of the sign, hooting and calling out "Peace DUDE!" in bad hippie accents.
Crystal clear.
Obvious.
Why?
Then Steve was being tackled to the ground, Tony screaming at him to "GET DOWN, GET DOWN!" The scientist's toned body plank stiff as he covered him and dragged Natasha and Bruce down by the backs of their shirts too.
The crowd had ducked, scattering in fear, when Tony screamed. Just as the Avengers had been taken by surprise and tried to fall into position, but Tony was oblivious to them outside of trying to drag the others onto the ground.
Screaming, crying, yelling himself hoarse.
"WAIT, WAIT, GIMME A GUN!"
Steve struggled under the panicking man, recognizing the full blown PTSD attack for what it was. He tried to catch Tony's hands from where they clawed at his shoulders and upper arms, tried to get them back onto their feet, while the rest of the team formed a protective circle around them.
"Tony! TONY!"
All over the news, in hours.
Tony had locked himself into his room as soon as they got back to the tower and refused to come out, apparently not even responding to JARVIS-though the AI assured the rest of the team that his vitals were normal, and scans hinted that he was just curled on his bed.
The others stared at Steve, obviously expecting him to have an explanation, but he could only stare at his friend's door, helpless and confused.
Pepper arrived within the first two hours, but was also rebuffed at the door.
Rhodey just about tripped up the stairs almost three hours after Pepper, breathing hard and still in his uniform.
"Tony?" He panted, looking from Avenger to Avenger, then accepting a hug from Pepper.
"He won't let us in," Pepper whispered, voice thick.
Rhodey leaned his head against the door for a moment, "Tony?"
A shuffling sound filtered out from behind the door, "Tony? Want to take a ride with me?"
The door cracked open, and Tony's voiced rasped out a broken, "Okay..."
When the two returned to the tower about half past nine, Tony tried to speak, opening and closing his mouth a few times, even a squeak emerging at one point, before he fled back to his room after throwing a pleading glance at Rhodey.
Tony's run across the room was embarrassed, defiant, and his movements were still jerky.
After the door clicked shut, Rhodey took a deep breath, and explained to them about a young soldier who'd just wanted a picture.
And the team agreed, right then and there, to drop the sign from their mannerisms.