1)Similar to a knee slapper. Basically an unfunny joke. Does not always have to be a pun. Name comes from lame dads who aren't great at coming up with very funny jokes, so when trying to look cool in front of their kids' friends.
1)uncool dad:"hey did you youngsters hear about the three legged dog?"
son/daughter (sarcastically):"No! Why don't you tell us about it!?"
dad:"well a three-legged dog in the old west walks into a saloon and says, 'I'm lookin for the man who shot my paw!'"
(nobody laughs, followed by awkward silence and cricket noises)
kid:"Wow, nice Dad Pun!"