Frust is Swedish word which describes the sounds you make when you are exhausted. For example: let's say that you missed your bus when you're already late for work. You decide to run to work instead of waiting for the next one to arrive. When you arrive at the office and discover that the elevator is broken you probably haven't reached the level of exhaustion that makes you frust. It's only after taking the stairs to your office at the 23rd floor that you really starts to frust. The frusting is best heard when trying to talk to people while in a condition of extreme exhaustion (example: if you meet your boss in the doorway after running up the stairs and he asks why you're late).