When something is particularly badass or exciting. The word is used to express amazement or admiration. It is often used in the same way as the word"swag".
Jeans-style is basically a 'one size fits all' adjective. When one is lost for words whilst describing something, the phrase jeans-stye will always suffice.
Guy 1: Hey man, you get it in last night?
Guy 2: Yeah man. Jeans-style!
Guy 1: Did you skip the test man?
Guy 2: Word. Jeans-style