"Believing his curiosity is merely sexual and aroused by his voyeurism, Dorothy makes Jeffrey undress at knifepoint and begins to fellate him before their encounter is interrupted by a knock at the door. Dorothy hides Jeffrey in the closet. From there he witnesses the visitor, Frank Booth (Dennis Hopper), inflict his bizarre sexual proclivities—which include inhaling an unidentified gas (possibly amyl nitrite), dry humping, and sadomasochism—upon Dorothy. Frank is an extremely foul-mouthed, violent sociopath whose orgasmic climax is a fit of both pleasure and rage. He continually refers to her as "Mommy" and to himself as both the "Daddy" and the "Baby", who "wants to fuck." Frank has kidnapped Dorothy's husband and son to force her to perform sexual favors; to "Do it for van Gogh." When Frank leaves, a sad and desperate Dorothy tries to seduce Jeffrey again and demands that he hit her, but when he refuses, she tells him to leave."

https://en.m.wikipedia.org/wiki/Blue_Velvet_(film)