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1.
An internal radar, thought to be instinctual, that determines the levels of sarcasm directly related to interactions with other people.
Derp: Wow those brussel sprouts smell amazing!
Derpette: What!?! Really!?! They smell gross.
Derp: Duh, I was just being sarcastic.
Serpette: Oh, sorry. My Sarcasmdar must be off today.
by CrazyCarter December 19, 2012
 
2.
a portmanteau of "sarcasm" and "radar", refers to the ability to recognize sarcasm in conversation. Similar to the use of "gaydar" (the ability to recognize someone's homosexuality)
Guy 1: Miryssa's cute, but she's kind of a ditz.
Guy 2: I know. But it's hilarious when she thinks people are actually mad at her when they're just being sarcastic.
Guy 1: Yeah, her sarcasmdar is totally defective.
by TheBloss May 09, 2013