When your lesbian lover is a self-described SADOMASOCHIST who's half your age, you've got to expect that not every night is going to involve relaxing on the couch with a glass of wine and some "NCIS".  But THIS is nuts. 


Last week, 23-year-old Mia McCarthy of Wellington, Florida was getting-it-on with her 52-year-old girlfriend.  Mia was using a VIBRATING ADULT TOY on her girlfriend . . . and kept on going even when her girlfriend said STOP. 


When she finally DID stop, the girlfriend called the POLICE . . . and Mia was arrested for sexual battery. 


Mia told the cops she's a sadomasochist, they were having, quote, "rough sex" . . . and she didn't stop because her girlfriend didn't use the SAFE WORD. 


Mia has also been charged for ANOTHER time things went too far, a few months ago, when she was choking her girlfriend during sex.