His friend challenged him to dance with the first girl he sees, and he saw you, so he reluctantly had to ask you to dance before the tango goes on

Kirishima: Ay, Bakugou! Hurry it up!

Katsuki: I know dammit, I'm gonna do it shitty-hair!

Denki: Ooooo!~

Katsuki walks up to you and takes your hand

Katsuki: IF YOU DON'T DANCE WITH ME I'LL KILL YOU! His signature glare

Sero: Dude...

Kirishima: He's going good so far!

Denki: Yeah if that's what you call manly? Laughs

Katsuki takes you to the dance floor