Remember ... Beetle's undefeated as an amateur boxer (remember when he fought Big Poppa?) ... and says he's truly confident he can hang with the top fighters in the sport, including Mike.
"Mike Tyson is a p***y," Beetlejuice said ... "He's scared of me."
Beetle -- who was out in NYC promoting his new Beetle's Juice E Juice -- also called out his longtime rival Floyd Mayweather ... a guy he's verbally sparred with on the Stern show before.
You gotta watch the clip ... dude may have better trash talk than Conor McGregor!