Rapper Dave East was arrested in Las Vegas. Police are charging him with domestic battery, after a threesome that went wrong.

According to a new report from TMZ, Dave East invited 2 women to his hotel room in Vegas last weekend - for a threesome. It was all good until Dave reportedly started giving one of the women more attention than the other, the police report states.

Then - the neglected woman went bonkers.

Here's what TMZ is saying:

Dave told cops she started hurling champagne bottles at him from across the room, and 2 of 'em made contact ... striking him in the head and leaving cuts -- which cops saw -- on his arm and leg.

As for the woman's version ... she told officers that in the middle of the sexual encounter, she and Dave got into an argument, and he threw punches 5-6 times, with one hitting her arm. She said she ran to the bathroom to call cops. She made no mention of bottles being thrown.

Dave is facing charges of domestic battery. If convicted - he may spend up to 2 years in prison.