Rosekiller
It was one of their friend groups birthdays, and it was almost midnight. Everybody was a little bit drunk, and Barty announced that they had to pair up to kiss at midnight. Regulus corrected him that that was only for New Years, but Barty insisted that it went for all celebrations. The others sided with Regulus, but Pandora decided that it would still be fun to do now. Dorcas called dibs on Pandora as she was the only girl, and Evan and Regulus paired up to spite Barty. Naturally, he just found another Slytherin who was open to kissing him, but before that he pouted for a solid five minutes.
From then on, it became a tradition in their group to always kiss at midnight, no matter the celebration. Pandora and Dorcas were always paired up because Dorcas is a lesbian, which left the boys to sort themselves out. After that first time, Barty was always competitive about getting a partner from their group. He always called for Regulus, much to Evans disappointment, as he had an unrequited crush on Barty at this point.
Regulus and Barty dated for a few months before deciding that they were better platonic and Barty began to fall for Evan. He had no problem with kissing Regulus platonically, but he would much prefer to kiss Evan and started asking to kiss him instead. Evan was shocked the first time this happened and more than a little scared. Now that the opportunity had presented itself, he realised it would be worse to kiss Barty and have it mean nothing to him that watch him kiss Regulus. He panicked and lied that he'd already asked someone else because he'd anticipated Barty choosing Regulus.
Barty could sense the lie and was devastated, but not discouraged. Every celebration, it became a race between him and Evan to choose a partner first, and Evan always won, choosing Regulus. This went on for a couple months and Barty had become convinced that Evan had a crush on Regulus. He vents about the situation to Dorcas, who has to stifle her laughter, having been playing the therapist to Evan about Barty for months. She decides to take matters into her own hands. The next celebration, she convinces Pandora to ask her crush (Lily Evans) to help her with the tradition, and she agrees. When it comes time for the others to decide their partners, she calls dibs on Regulus, much to everyone's surprise.
At midnight, Evan and Barty kiss for the first time, and pretty much immediately after, Barty confesses to Evan who bursts out laughing, realising what Dorcas has done. They start dating and Dorcas takes the credit any time she can.
"I kissed a dude for you guys".