Airplane was the earliest I can think of.
Constantine had a post credit scene.
Airplane was the earliest I can think of.
Constantine had a post credit scene.
James Gunn's horror movie Slither had one 2 years before the first Iron Man movie came out.
Super Mario Bros. had Iggy and Spike pitch a video game to Japanese game designers about 'their' adventures, the Super Koopa Cousins.
EDIT: Here's a list! It looks like the first one ever was from The Silencers. https://en.wikipedia.org/wiki/List_o...credits_scenes