Society expects men to like and do certain things, and women to like and do other things. Of course, the majority of things overlap, but if you're a guy and you like to do things that girls tend to like doing more, you're suddenly labelled as being gay or sissy. If you're a girl and like doing things that guys tend to like doing, you're labelled as a tomboy or in extreme cases, a lesbian. I've seen cases of this and it's quite irritating. I feel people should be able to do what they want to do without worrying about being thought of as gay when they're not (or vice versa!).

For an example of this that really pisses me off, see people who think male catlovers are gay.