If you are referring to lady gaga, It could be just about anything.
It could be just a term for dancing very close together, that kind of naughty grinding stuff that younger people are doing these days on the dance floor.
Disco stick could be a kind of dance, that only she knows about. Like the hustle, or the bump. It could be just an attitude. like getting your poker face on.
but, could be a penis. who knows LOL!!!