A person or thing which takes a ridiculous amount of time to perform a certain task, esp. in the instance of causing someone to have to wait for a very long time. Originally named after the infamous pro wrestling championship belt company JMAR, which is known for literally taking years to make belts for clients.
I ended up waiting at the store forever because the lady at the check out was such a JMAR.
This slow ass computer is being a JMAR.
I was late to work because I got stuck driving behind some JMAR.