Kathy Griffin -- Mum on Cryptic Stephen Collins Tweet ... Who's Jack M?

Kathy Griffin was mum about her mysterious tweet ... suggesting there's someone else out there who should be really worried about getting busted for child molestation.

Griffin weighed in on the Collins child molestation scandal Tuesday when she tweeted, "Well well well #StephenCollins, looks like u may have finally gotten urself busted after all these years. Jack M, ur next? KG"

It left people wondering ... what did Kathy know about Collins and who in the world is Jack M?

But when we asked Kathy about it Wednesday night outside Osteria Mozza, the boisterous comedienne kept her mouth shut.