When you walk in onyour brother (could also be a friend) getting a blow job in your room. It could also apply to other sexual activities.
Ryan: so I walked into my room last night and mary was proving that her milkshake brings all the boys to the yard to my brother.
Callie:Wow! what a slut!!! you should have been like, "now thats a thanks bro if I've ever seen one!"
