When a man ejaculates onto a women’s face.

When a man nuts on a woman's, the semen on her face represents a baby thereby naming her babyface

A person who can’t grow an itch of facial hair

When a girl who usually wears a flawless full face of makeup goes without any product, usually while running errands, and the contrast is significant. Dark under-eye circles, blemishes, and washed-out looking skin combine with small-looking eyes (from no eye makeup) to create a face like a newborn rodent or "baby hamster face".

An expression used when someone says or does something entirely stupid. The expression is related to someone having unprotected sex at a young age and getting knocked-up. Yeah, probably one of the stupidest things you could do. Getting knocked-up leads to babies, and so when someone says/does something really dumb, throw a baby at their face because if they want to do something that stupid, they'll probably end up doing even more stupid things like... oh, getting themselves pregnant. Just, don't really throw a baby at their face, it might harm the infant.

The "her" can be interchangeable to "his" or "their"