When you're trying to get it in with a lady, and it's suddenly time to go ( because your ride is here/ the place closes/ it's time for her to leave etc. ) and you end up never getting to do anything with her.
Girl: I so wanna fuck you right now!
You: oh baby, let's do it!
Girl: Oh shit my moms here to pick me up, I gotta go!
Your friend: Well shit dude, Id say you just got clockblocked!
In basketball when you make a shot off the shot clock and it doesn't count or having a made shot called off because of not getting the shot off in time.
I thought I hit the game winning shot as time expired but I was clockblocked by the buzzer.