Girl's Behavior

Girls, Why is my girlfriend so upset over a joke?

We've been together for a good 4 years now so we know how we both are with jokes and silly stuff. We're always saying something completely off basis and random to eachother which sorta completes our relationship but this weekend she ended up getting really upset from a very obvious joke. We were staying at a hotel for a few days to visit somewhere. We were cuddling and then ended up hearing our hotel neighbor next door going at it for a little bit which was pretty funny to the both of us because we had no idea our hotel would have sorta thin walls like that. I ended up saying we should do a foursome as an very obvious joke because not even that long ago she was just joking about hoping to see a certain cashier guy at dollar tree who looks at her boobs when buying her stuff. I really have no idea why she got so mad for. Even went as far as to open up a beer and start drinking which was kinda mind blowing to me. I asked her why she got so mad for and she said it was a nasty joke. I replied you make jokes like that all the time and then she got silent. I'm just so confused.

Girls, Why is my girlfriend so upset over a joke?
Post Opinion