Here are some randomly selected joke topics beginning with the letter 'O'
Over an hour
Knock, knock.
Who's there!
Ben Hur who?
Ben Hur for over an hour - let me in!
Owl
Knock, knock.
Who's there?
Owl.
Owl who?
Owl aboard!
Outlaws
When Marriage is Outlawed,
Only Outlaws will have Inlaws.
Overtime
Why did the baker work overtime?
Because he kneaded the dough.
Overweight
You know you're overweight and need to diet when your knees buckle but your belt won't.
Outlaws
What do baby outlaws like eating with their milk?
Crookies.
Overweight
Overweight just sorta of snacks up on you.
Overweight
What do you call an overweight ET?
An extra cholesterol.
Owl
What do you get if you cross a ghost with an owl?
A creature that frightens people but doesn't give a hoot.