Having intercourse

A phrase for "having class in between" but you are tired of being invited by your friends, so you want to say the reason in a sexual way...
(Course = class and inter = in between)

A: Hey! Join us on Discord now! We have a lot of things to discuss!
B: *No reaction*
A: *Spam dots*
B: Not now! M8! I'm having intercourse right now! Lemme finish it first!
A: Wow! Ok! I understand... hehe