Play video content EXCLUSIVE

You don't attack the Church of Scientology and get away with it ... not by a long shot -- so says one famous ex-Scientologist Vince Offer (the ShamWow Guy), who tells TMZ, Leah Remini is lucky she's still alive.

Offer was out in L.A last night -- and it's clear he's still concerned about L. Ron Hubbard's followers after his highly-publicized split from the Church ten years ago ... because he was VERY hesitant to talk about Remini's situation.

You'll recall, the "King of Queens" actress recently left the Church, then filed a missing persons report regarding Shelly Miscavige, the wife of Scientology leader David Miscavige. The Church was PISSED.

Offer called Remini's move "brave," but said he couldn't say much more because he values his life ... and he wasn't kidding. You have to see how scared this guy is.