To Keian someone is a verb meaning to promise or act like you are going to do something, see something, go somewhere etc... and then to not full-fill said promise.
It can also mean to be consistently unreliable.
Past tense - Keian'd
Person1:"Hey man, is Tommy coming to the party?"
Person2:"Yeah, he said he'd come this morning.."
*Half way through the party*
Person1:"I think Tommy totally Keian'd you man.."
Person2:"Yeah, he's so unreliable"