loaded weapon 1

No, that's part of the joke. By putting a 1 after the title, they give the idea there is a number 2, which isn't.

I also think it is a parody on the many number of Lethal Weapon movies.

No, just a spoof of the Lethal Weapon Movies.


They also had this joke with Mel Brooks's 'History of the WOrld, Part 1.' There was no part 2.

I have something I want to say to Idocamstuf. You are a complete and utter idiot. You have the nerve to make an insult about anything, much less a National Lampoon movie, and you think that anyone will take someone seriously who can't even spell crap right? C-R-A-P. There's only one P in it Primordial Ooze. I suggest you rent Mavis Beacon Teaches Typing before you rent any more movies and think that anyone cares what you have to say.

It's a joke, man! Like how many times do people end up saying "1" after the title of movies which later get a sequel? E.g. Rocky, it isn't called "Rocky 1" but when you end up listing them that's what it gets called, it happens all the time, so I guess the writers just figured they'd put the "1" there as a gag, because sequel or no sequel that is how it would be known, One question though, How often do you call it "Loaded Weapon 1" as opposed to just "Loaded Weapon"?
See? You take the "1" away because there's no sequel but if there was, well in this case it would already be there but with other movies you end up adding the "1" It's just the way it works.