A person who functions on a lesser level of mentality than most bean sprouts. These people are characterized by their innane questions and poor use of grammar and sentence structure. Also, when confronted with situations they cannot comprehend (example: A sum of money IS required in exchange for the temporary use of a rental vehicle), they will become enraged and counter with random, irrational screaming. These people are typically met over the telephone, and are best deterred by such methods as hanging up, or, making farting noises into the receiver until the said person becomes so frustrated by the lack of attention to their ranting that they hang up.
"I was speaking to a rental car customer, and they were upset that the location would not accept their check cashin' cawd...Oh dammit I hate these people! Shoot me!!"
First definition: One who's reservation is not held.
Second definition: Hopeless victim, who, after driving a creaky, smoke-filled vehicle with dome lights out and mysterious engine clanks, cannot contact anyone at the rental car office but an uneducated twit who couldn't make it as a used car salesman.
That guy standing by the broken down Escort? Yeah, he's one of our Rental Car Customers.