Nikki Bella says she was PISSED WWE decided to introduce Ronda Rousey on the night of an historic all-women's event ... calling the move "a bit of a slap in the face" to the female wrestlers that came before her.
Of course, WWE hosted it's inaugural ladies-only Royal Rumble in Jan. 2018 ... with 30 wrestlers (including Nikki) duking it out for an hour straight. After the Rumble, "Rowdy" Ronda Rousey came out of the tunnel for the first time ever and pointed to a Wrestlemania sign hanging in the rafters.
The moment was supposed to tease Ronda's wrestling debut -- which went down at Mania in April '18 -- but Nikki felt the move essentially stole thunder from the history-making Rumble.