In the spirit of Cussing in German, here come Cursing in French French (as opposed to Canadian French), and let me start by saying that only dipshits would spell it cussing.
con: cunt, used for virtually anything. "C'est con": it's too bad. "T'es con": you're stupid. "T'es vraiment trop con": you're really fucking stupid.
foutre: fuck, although not used as in "let's fuck", unless you're reading Sade. "Va te faire foutre": go fuck yourself. "Rien à foutre": I don't give a fuck.
pédé: gay, fag.
enculé: someone who likes to take it up the ass. Very common (the expression, I mean)
merde: shit. As mentioned in Cussing in German, nobody give a flying rotating shit about people cursing in France, at least not as much as in that fucking retarded country called USA, so that's something (merde) you can use liberally here.
putain, pute: whore. Very common. "Putain, ça fait chier!": fuck, that sucks.
chier: to shit.
ça fait chier: it sucks.
pouffiasse, pétasse: bimbo.
cul: ass. "J'en ai plein le cul": I'm fed up with that shit.
baiser: to fuck. "On s'est fait baiser!": we're fucked.
niquer: to fuck (from forniquer). "Je suis niqué!": I'm fucked.
suce ma bite: suck my dick.