This is someone who basically abuses your trust. Also knows as 'T.A.' A 'trust abuser' table for your friends can be made, to see who is the worst offender. Our leader by a million miles is Anthony the number one T.A.
A person says they will come to the pub with you and then at the last minute pull out of going after you have arranged it. This is an abuse of your trust, therefore a 'trust abuser.'