Marilyn Manson -- Grand Slammed in the Face at a Denny's

Goth rocker Marilyn Manson got more than two pancakes, two eggs, two pieces of bacon and two sausage links during a trip to Denny's this past weekend ... he allegedly got clocked in the face!

According to our sources, Manson had a concert in Alberta, Canada on Saturday night and hit up a local Denny's around 2 AM. We're told Manson got into an argument with a group at another table, and at some point allegedly called a guy's gf a bitch.

The guy was pissed, and we're told he responded by punching Manson in the face.

Police confirm there was a disturbance at Denny's that night, but no charges were filed and the case is closed.

We've reached out to Manson, and he's going on the attack for what he calls a "sucker punch."