Shitting the Door

When people are scared it is said they'll 'shit their pants' and when people are emotionally distant it's called 'putting up a wall' (or door in this case.) Shitting the door simply means you are scared to get emotionally close to someone so you put up a door to prevent that.

Boy 1: I really like Becky but she doesn't seem to like me back...
Boy 2: Nah man, she's just shitting the door. Give her time.