Sucking on Big Balls

Listen up, buttercup. This joke is all about the "big balls" which is a euphemism for testicles. The joke teller mentions they like, ahem, 'sucking' on them and then says they're gay 'af' (as fuck) -- implying a same-sex attraction, which is what makes it funny. As you probably already know, since you like this kind of humor so much, you likely can't get a date.