earthquake battery
A fact you claim to know, even though you just guessed it and hope no one asks you to prove it.
'I’m 100% sure I heard that on the radio!', said by someone who just turned the radio off.
'You don’t believe me? I’ll believe myself and you’ll be wrong.', said by someone who’s never been right.
'I didn’t make it up, I just got it from a friend who got it from a friend.', said by someone who’s been wrong for years.