My girlfriend gets pissed off by "sexist" jokes, is this normal?

No it isn’t normal. Your girlfriend has issues and is insecure. A sense of humor can go a long way. I’d seriously look at moving on from her. This will likely spread to other areas in personal life

Omg tell her to calm down. 

It is interesting.  My wife laughs with me about sexist jokes, we laugh at things like the "Benny hill show" or the carry on series.  Sex is fun and it is funny.  Many women today have forgotten this entirely.

Your GF sounds like you're typical karen, don't settle for a woman who will place restrictions on you.

It may be normal to scoff at something like that but not to carry it around all day and let it ruin your life. What's probably going on here is that she's irritated with you but instead of using her words to address her real beef she's indulging in a generalized victim mentality hoping you'll catch on and stop doing whatever it is you're doing that she doesn't like. Maybe ask her about it and tell her you don't really believe she stays mad all day over an off color joke. 

So what's the joke? It's probably funny. 

Edit: Female comedians tell period jokes all the time. lol

touchy, touchy. she must be a liberal. they have no sense of humor and can't laugh at themselves. they are the reason we have no funny comedians any more. everything is offensive! call the PC police! ugh!

I totally agree with your girlfriend.  Any joke or prank that makes other people feel inferior or stupid is not funny to the subject.  And guys who do this all the time show a huge disregard for women.