Internet playboys Nik Richie and Dan Bilzerian have been trading barbs online for months and they finally came to blows Wednesday night … well, not really … but it's hysterical anyway.

Richie was celebrating his birthday at Surrender Nightclub in Encore at Wynn Las Vegas when the club brought him out a birthday cake … with Bilzerian's bearded mug on it.

Rather than blow out the candles and cut the cake, Richie put on a pair of boxing gloves and pummeled it.

NR and DB have been going back and forth for months about fighting -- Nik wants a boxing match, Dan wants it MMA. The stakes? In the hundreds of thousands of dollars.

Bilzerian tells TMZ, "If I ever got a birthday cake with another dude on it, so I could hit it with a boxing glove after I had refused to fight him for 200K, I'd know I lost at life."