Those are words that are used an awful lot. Sometimes bullies say them to try to minimize or excuse what they've said or done. Sometimes the person saying it might genuinely not have intended what they said or did to be hurtful.
Some things just plain are not jokes. Telling someone they're fat, ugly, stupid, etc. is not humorous by any stretch of the imagination. Calling someone a fag or a retard? Not only not funny, but not acceptable.
In schools, kids say cruel things to each other. Supposedly it's just part of growing up. My point is that it shouldn't be. No one should have to deal with being called "Elephant Girl" because she has trouble walking. (Yes, that happened to me.) No one should ever be called any of the things that I mentioned in the previous paragraph.
Actions like shoving someone into a locker or throwing a slushie on someone--which I hope hasn't happened to anyone outside the show Glee, and I kind of wish it didn't happen on that show because they make a joke out of it-- aren't funny either.
The next time you think you (or your child if you're a parent) are "just kidding", stop and think about whether you'd laugh if it was said or done to you. If not, don't say it or do it to someone else.