Generally a bad idea, especially if there had been intimacy. Being friends with ex will limit your chances of future relationships. I would say, do be acquaintance if you have mutual friends, but try not to meet up even in groups.

would it be weird if you had many crazy sexual intercourse with your ex before and after break up still be friends? A bit awkward.
If never touchy touchy after breakup still be friends very easy la.

Nope doesn't work at all. Even though the break up may be mutual, there will always be some form of scars. Being human, we always choose the easier path which is to forget away. With that being said naturally after break up, shy away from each other until all is forgotten that is if it can be forgotten.

how true!

follow your heart bro...but just don't get heartbroken