twat cred: when you already think someone is an idiot, and they show you another example of why you hold that opinion.
Background: "Twat cred" is a play off of the common term "street cred" which is short for "street credibility" or street reputation.
"Twat" is a term orginally meanining "vagina," but is often used to describe someone who's an idiot or a general dirtbag.
"Dave and Mike think all brown skinned people 'grew up on tacos,' once again proving their twat cred."
"Sarah threatened to fight the neighbor when she argued about the newspaper missing from the steps, showing her real twat cred."