Pertaining to a kid that is so obnoxious it makes you never want to have kids especially through the use of birth control / rubbers. Hence “Rubber Baby”
Person 1: I went to my friend's house and their son is so out of control. He bit me seven times and punched me in the nuts twice.
Person 2 : I know me and my girlfriend were over there Saturday and it was enough to make us start using condoms
person 1 : Yeah he’s a real Rubber Baby
Source: deck man, stl