Shaq -- 'Big Show Is Scared' ... 'I'm Coming For You!'

Shaquille O'Neal has a message for WWE honcho Vince McMahon -- SET UP THE FIGHT WITH BIG SHOW!!!

Shaq was out in NYC -- and told us he's dead serious about wanting a piece of Big Show at an upcoming WWE event.

You'll recall, they tried to chokeslam each other at WrestleMania earlier this month -- and then called out the other in the aftermath.

Now, Shaq says he wants the McMahons to make it happen -- and has a special message for his 7-foot rival ... "I'M COMING FOR YOU!!!"