When someone thinks they are the best, most coolest person ever when really they look like a tool.
Bob thought he was topshit driving his brand new hatchback down the road.
Someone or Some people who have a high social status and are determined 'popular'.
Have you seen that gus guy, he's pretty topshit.
Merchandise and items usually sold in Topshop
They're having a sale to get rid of the topshit.