Bo-yah is a fun way to say Oh yeah. It is usually associated with one subject agreeing with or supporting anothers thought.
Hey Brad, do you want to go to the concert this weekend??
Brad: Bo yah!
Big crime is a cooler way of saying Big time, which is a cooler way of saying yes.
Hey Timmy, were the fish biting today?
Timmy: Bo yah.. big crime!!!
Translation: "yes, i got alot of bites"