There's a Young Thinker story called At UC with some similar elements.
In it, guy is tired of his girlfriend clubbing then passing out, so they go to a bar his friends recommend. The bar has an amateur night and when his GF is distracted he sees his younger sister (former cheerleader, now 22) up on stage, so he dances with her.
No one who knows either of them knows they're siblings, so they get a bit wild with their flirtation. Owner loves it and offers them a job as semi-professional dancers to get the amateur nights going wild.
Unfortunately, Young Thinker pulled all his stories off SOL a few years ago, so finding it will require a bit of legwork. A few stories are on ASSTR, but not that one.