I saw a movie when I was about 5 years old, and the cartoonish antagonist in it became the monster under my bed. Here's what I remember:
Saw it in circa 1983, probably on HBO; I don't think it came out more than a year or two earlier. Probably American.
Low budget, probably direct-to-video.
Spaceship crew on some sort of mission, discovers alien life.
Alien is a one-eyed mass of red slime.
At least one woman on the crew.
The alien is placed in a containment unit with glass walls. Doctor/scientist assures crew that the alien is intelligent and friendly. He puts a device on the alien's head that translates its thoughts into English speech. The alien proceeds to do a song and dance routine, with lyrics about how much he wants to eat the crew. His voice sounds like Barry Manilow.
The doctor/scientist is oblivious to this explicit declaration of hostile intent, and assures the crew that the alien is, as he had already said, harmless. He enters the containment unit and the alien immediately tears off his arm and eats it. Very reminiscent of the Black Knight scene from Monty Python and the Quest for the Holy Grail. The doctor/scientist insists that the alien is merely playing. He is then devoured outright, with the possible exception of his calves and feet.
Alien goes on the rampage, eating the crew members one by one. Eventually, one or two survivors manage to eject the alien through an airlock.
The movie ends with the ship flying through space, and the words "The End" appearing on the screen. The camera pans out and we see the alien floating along behind the ship, and a question mark appears behind the caption - "The End?"
It was clearly a campy parody of Alien, and the production values, acting, writing, sets, and dialogue were absolutely appalling. In short, it shouldn't have frightened me at all, but I was a huge baby, so it utterly terrified me. I was probably the only person who was scared by it, and I imagine that there are no more than a few thousand other people who have seen it; I am absolutely certain that none of them enjoyed it in the slightest.