What do you call a lump of dust that you don't need?
YOUR PARENTS... SO KILL THEM IN THEIR SLEEP.
...but didn't find any of your others funny. I'm not sure why. The punchlines just don't work for me. The best suggestion I can think of right now is to make sure you know what the punchline is going to be before you write the rest of the comic. You have some potentially funny ideas, but it seems like you don't use them well enough.
--- The what mentioned above is total fiction. Please don't take it seriously!