Ronda Rousey to Rival -- Enjoy Your Mommy Time, I'm Still Gonna Crush You

UFC champ Ronda Rousey is making it clear to her next victim opponent -- she can play nice outside of the octagon, but inside ... she'll still bash in her face.

Ronda's warning went out to fellow UFC fighter Cat Zingano ... who's going head-to-head with Rousey as a coach on the next season of "The Ultimate Fighter".

They're also going to compete in a title fight.

Zingano had the stones to tweet Rousey today, asking if she can have all the early training times while shooting 'TUF' ... so Cat can spend more time with her son.

Rousey tells TMZ ... despite her usual desire to torment the competition at every opportunity, she's willing to make an exception and grant the mommy time.

But Ronda also cautions Cat ... "Enjoy the convenience of your free time in the afternoon and evenings, but don't expect me to be so nice the night of the fight!”

Translation ... mommies get no mercy.