'Fifty Shades of Grey' Trailer -- Hardcore BDSM Crowd Left Limp

The first trailer for mommy porn "Fifty Shades of Grey" might be exciting some lonely fans -- but serious BDSMers aren't ready to peg the movie for success ... because to them it kinda looks like amateur hour in the ole dungeon.

Don't ask how, but TMZ got in tight with some members of the Threshold Society -- a BDSM/leather club in L.A. -- and they say overall reaction to the trailer is ... where's the good stuff???

Threshold's corporate secretary (for reals) Azurell says the buzz from members is there are tons of other books and movies that better reflect their lifestyle -- and based on this first taste ... 'Grey' looks kinda "vanilla."

Azurell adds ... the movie could use more of their specialties -- light bondage, caning, needle play, fire play, and pegging. We're not telling you to Google that last one. Especially at work.

Over at Hollywood's Bar Sinister ... pro dom Feenix says 'Grey' has gotten a rise out of people in their 40s. He says more middle-aged couples are lining up for their loft area. Think VIP ... for people who want a good spanking. Or a bad one.

Seriously, don't look up pegging.