I don't think cheating is that bad
Why don't you think cheating is bad?
I want to make a person feel bad about their gf
Cheating is bad, because it is a betrayal of trust between two people. You should not want to make someone feel bad at all.
Isn't it funny when someone finds out they were cheated on?
I do not think that is funny at all. How would you feel if you were cheated on? I do not think you would think that funny.