I usually try to be a bit more eloquent in my reviews but genuinely all I can say about Bad and Crazy is I fucking loved it.
It's super wild, so funny, and such a good time. Lee Dong Wook and Wi Ha Joon are an amazing pair and the bromance is top-tier. The villains are awesome, too. Boss Yong especially is a great character. I didn't think it was all as predictable as I've seen others say it is but it's true I don't tend to try and predict what's going to happen.
I think if you tend to be more on the skeptical side and looking for realism, you do need to get into it with an open mind and remember that we're following Ryu Soo Yeol. We're following him 95% of the time, seeing what he's seeing. If you're thinking "wait, this doesn't work," in my opinion yes it does, in Ryu Soo Yeol's head it does.
I would highly recommend Bad and Crazy, especially if you need a break from more mellow dramas or romance, and are looking for something a little more... well, crazy.