Sometimes I overseason my girlfriend's meals.
Why do you think it's okay to mess with your girlfriend's meals? You should want her to enjoy them, right?
She gets mad and I think it's funny.
I have a partner that sometimes I just do some petty things against him as well, but this is your significant other that we're talking about and she has feelings and she may be really looking forward with the food that you're cooking for her. So how about you don't over season her food, and cook it the best way that you can so that she can be happy?
I'm not changing my mind about this. I've been bored with the relationship, so making her behave like a bitch is the fun part.
Overseasoning her food when you know it makes her mad isn't nice. Being mean just for fun is rude and it's not part of a healthy relationship. If you're so bored you're being cruel, you should end the relationship.