alien invasion theme, I have to make a big exception for the 1988 film Killer Klowns from Outer Space.
With a title like that, you know you're not sitting down to a movie of even a Hollywood level of seriousness. This is pure parody from start to finish, and effective parody too. All the elements of the genre are here--the alien invaders, the teens who know more than the adults, no one taking the teens seriously (this time for the forgivable reason that the aliens are clowns) and the plucky kids going off to defeat the aliens on their own. . .in an ice cream truck.
So if you are a fan of b-movies, check this out. Where else can you see dead bodies wrapped in cocoons of cotton candy?