Are we allowed to curse on Lichess chat/forums?

Don't want to get banned over something stupid like that

You can, but your not really supposed to

It's not like I want to swear at everyone, just wondering if I have to filter myself at all

Swearing isn't an offense for which you would ordinarily be banned; you'd either have to take it to a ridiculous extreme (I can't even think of a way to really do this), or be openly/actively harassing users (more likely). At any rate, we're all (well, many of us are) intelligent adults, and unless you're being *really* egregious about it, the admins (I think thibault said something to this effect once) don't give a fuck. :)

so long as it isn't intended to offend and it's not excessive.

ex: fuck! my crystal chessboard fell on the sidewalk
vs
your mother is a fucking potato

(second one has the intent to offend)

But then again, they're many other words that can replace swear words.

"Swearing isn't excessively prohibited, but ask anyone and they'll agree that there's a clear cut between a friendly "shit, I blundered my queen" or "missed the fucking win", and offensive insults."
- Unihedron, in "An open letter about the Cheater Investigation Association"