Girls and guys have different ideas of what a "good dancer" is
Guys often see dancing as a skill to show off. Being 'better' than other dancers is important to them. Their typical image of a good dancer is a gymnastic break dancer doing a bunch of flips, or a guy doing a fancy, fluid Popping and Locking routine.A girl's picture of a good dancer is a closer to a passably moving guy who looks comfortable, confident, and like he's having fun. Lots of girls have told me I'm a "good dancer" (i.e., I'm actually dancing, and not like a total fool), but not many guys have.
Don't worry about what guys think. Sometimes guys will snicker and point to people who are dancing because they're really just uncomfortable about doing it themselves. Random dudes sucking on their beer aren't your audience.
