Pietro went to sneak into the X mansion through the back door and went to head for the professor's office. But suddenly lots of hands wrapped around his wrists and he was tugged back coming to face most of the X men, "hey, what are you doing!?" He asked, he went to tug away but was pushed back into a cupboard. The students thought this was funny when they closed the door and locked him in the tiny space.
As a speedster, he had to have room to run and this would make him extremely claustrophobic if he didn't, plus he was also claustrophobic before he got his powers so this was one of the most horrifying things that could happen to him. His eyes were darting around the room. The walls were closing in, he screamed and pounded on the the door for them to let him out but it was no use all he heard was snickers on the other end. "Teaches you for sneaking into our home!" He heard Scott shout, he sunk to the ground and curled up in a ball, he started crying silently and rocking back and forth.
He heard some say, "do you think he's, like, ok, it's, like, dead silent in there," it was Kitty,
Someone else said, "oh, come on, this is PIETRO we're talking about here, he's probably doing that just to get his way." He heard them all walk away from the door and he was too scared to even shout for them to let him out. He just sat there rocking back and forth fearing that he'll run out of oxygen or the walls will crush him.
MEANWHILE WITH THE X MEN...
The group of X men that locked Pietro in the wardrobe walked off laughing. They went off and did their own thing for half an hour not even once thinking about the boy captive in the cupboard. Only when professor Xavier asked everyone if they had seen Pietro because they were meeting for lunch, did everyone involved panic. When professor X went to them and saw that Kitty was twirling her hair nervously he asked her personally if she knew where he was, she cracked and said who was involved.
He summoned everyone involved and made them take him to Pietro, when they got there, they opened the door slowly and saw something they would never imagine. Pietro was curled into a ball rocking back and forth with his head in his knees whispering things about the walls closing in on him. Only when the door was open fully did he rush out and say, "next time we meet, we meet somewhere else." And zoom off.