"
let's rejoice with the boys in the gay way
It's okay to be gay, let's have anal sex.
Rejoice means have joyful fun, and the boys are obviously men.
After that it says in the gay way, so all together, that means:
"Let's have 'fun' the gay way with some men! Considering it's a song about being gay, it obviously refers to sex, and as men can only have anal sex, then the whole phrase is basically:
"Let's have anal sex!"