When you don't have any money, you are low on cash, without funds, or just plain old "financially embarrased.
Hey girlfriend, me and my girls are going to check out that new movie, so how 'bout you? Sounds fun, but I can't this time cause I'm riding the greyhound.
My girlfriends went to the movies tonight, but I didn't go with them cause I'm ridin' the greyhound
til I pick up my check from work.