Floyd Mayweather Jr.'s Baby Mama to GF -- Karma's a Bitch ... And So Is Floyd's Penis

Floyd Mayweather Jr.'s current GF better not get too comfortable ... because the boxing legend is banging at least SEVEN other women behind her back -- so claims Floyd's baby mama Josie Harris.

Harris called in to "TMZ Live" today to explain her beef with Floyd's on-again-off-again girlfriend Shantel Jackson, after Jackson allegedly ripped off her 10-year-old daughter's dress at the big fight in Vegas on Saturday ... but the beef wasn't the bombshell.

Harris is clearly pissed, but says Jackson has bigger things to worry about than some 10-year-old's dress ... namely Floyd's parade of women he's banging on the side. You gotta watch the clip!

All that said ... Harris still feels the designer who sold Jackson the same dress committed a "cardinal sin" in the fashion world. Listen below.