This word is used very often in the North East of England. Especially by teenagers on the streets and chavs. It's basically just used as a substitute for words meaning cool, class and ace.
thats proper mint that!
woahh man thats mint as!
An expression that, in terms of classifieds advertising, has lost all meaning.
Trying to sell my <item>, used only a few times... in mint condition!
If something is a mint, it makes a lot of cents, or in this case sense.
*after explaining something*
reply: Woah bro ok thats a mint!