This is from the "One time..." prompt list on Tumblr.
"One time he got punched by Bill Jr."
It all happened too fast. One moment he greeted Bill and the other he was spitting blood into the palm of his hand.
"Bill! What the fuck?!" Scully exclaimed.
Mulder stared at the tall red headed man. He had his fists clenched looking down at Mulder.
"What's wrong with you?" Scully stood in front of Bill.
"How dare you bring this man to OUR family reunion?" Bill Jr. pointed at Mulder accusingly.
"'Cause he's part of my family."
"How is your work partner family?" Bill asked mockingly.
"He's my boyfriend!"
Scully left them all in shock. She grabbed his free hand, the one that wasn't holding a handkerchief to his mouth, and dragged him upstairs.
She pulled him inside a bathroom and locked the door closed. Her hand went to cup his cheek. Her thumb caressing the skin there. Mulder hissed and she pulled her hand.
"Are you alright? Let me see." He gave her the blood stained handkerchief. His bottom lip looked a bit swollen. His cheek was turning a bit purple.
"Look I'm sorr-"
Scully cut him off. "What are you sorry for? You didn't do anything." Mulder shrugged. "Don't say you're sorry you're here. I'm sorry you didn't hit him back."
"Your mother was there. I couldn- wouldn't."
He stood leaning against the sink. She leaned against his chest and just stood there.
"I'm your boyfriend huh?"