Blac Chyna Not to Blame for Poor Sex Tape Performance, Claims Expert

Blac Chyna's not the only one who blew it with her sex tape performance -- her ex-BF's lazy attitude is just as much to blame ... according to the sex expert, the "Head Doctor."

Chyna's been slammed online since the video with Mechie leaked, with critics calling her effort uninspired and boring. That's an unfair review though, if you ask Ms. Preasha -- aka "The Head Doctor" -- and we did. She's pointing the finger at Mechie for a lack of effort.

Preasha, who presents workshops with her company, Legendary Oral, says good fellatio takes 2 -- people that is -- and Mechie didn't hold up his end.