What does "If you're gonna get up in my face you'd better be ready to back it up!" mean?

I just read the following expression: I have a vague idea what it means but please could a native speaker comment:

"If you're gonna get up in my face you'd better be ready to back it up!"

Solution 1:

The first part is idiomatic:

Get up in my face

This refers to the way that someone acting aggressively will often get very close to their opponent and shout in their face. Figuratively speaking, it can also just mean someone being aggressive or antagonistic, without them necessarily getting physically close.

back it up

Means acting on the aggression physically, in this context.

So the whole phrase means:

If you are willing to talk aggressively, you had better be ready to fight too.

The implication is that they had better be ready to fight, because the speaker is.

Solution 2:

It means - if you are going to confront me, you should be prepared to fight.

"In my face" means (literally or figuratively) standing face to face within the distance normally considered "personal space" and reserved for contact with close friends. If someone who is not a close friend does this, it is considered aggressive.

"ready to back it up" is a vague cliche that suggests having available supportive material, reasoning or (depending on context) force.

To back someone up is to stand behind them ready to provide assistance.

Solution 3:

My guess is it is ADDITIONALLY a play on words
Face: front of you
Back: behind you

It rolls off the tongue like Monty Python's "If you're going to split hairs, I'm going to piss off."