Let's not forget the cool 26 different mini shmup games included in Namco's Tenkomori Shooting/Tenkomori Variety Shooting PCB. There's even a Time Crisis themed mini shmup to play! Crazy game to play with a partner indeed. Can you rescue your kidnapped baby kid brother from the clutches of an evil witch?
I think the shooter that has made me laugh the most is Jikkyou Oshaberi Parodius. It's just so bizarre. The Chou Aniki games is a close second, but that's more like a confused/disturbed laugh inducing game.
"Management qualification of a new star machine is only given to a grades that is excellent."
Also, it's sort of funny how in Level 15 you have all the little wee tanks rolling along in a column firing at you, and then out of nowhere the boss rolls in and runs over them.
Dimahoo's also pretty funny in that sense, though you don't get point items for that kind of thing, so there's no point in letting, say, that excavator drill its way straight through the wall of small green tanks (Which also attempt to escape the path, but only for naught).
Metal Slug and Elevator Action returns gets my vote for run-n-gun. The whole outhouse scene and the pyros running like heck from a crashing helcopter are good. Oh and The Outfoxies is funny in the end when you kill the Acmes.