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1. The useless, red, watery substance that comes out of a ketchup bottle when one forgot to first shake the bottle and thus ruins your fries, your burger, or whatever else you wanted it for.

2. An insult levied towards an undeserving individual who is both a "one-upper" and a narcissist; one who is useless and ruins a great time together with friends and/or family.
1. That restaurant has THE BEST French fries. When they finally served them, I eagerly grabbed the ketchup to enjoy God's gift to man. But all that came out of the bottle was Diarrhetchup; ruining my fries!

2. While I was discussing my Slavic lineage, that Diarrhetchup butted in the conversation to say how awesome it was being French.
by Game-Player December 21, 2015
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