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3.
1. A phrase used to indicate one's negative feelings regarding a proposed situation.

2. A courteous declination to an unpleasant proposition.
Dude #1: "Hey, man. How would you like to spend a night with that beast?!?"
Dude #2: "I'm thinkin' Arby's!"

Friend #1: "What do you think about going to Kevin's place after the game?"
Friend #2: "No way, dude. Kevin's a jerk! I'm thinkin' Arby's."
by aksival December 16, 2006
 
1.
A phrase you utter when you see a woman whom you suspect of having beef curtains. (A play on a popular food chain's slogan.)
Newscaster: "A 60 year old prostitute was arrested today..."
You: "I'm Thinkin' Arby's."
Your friend: "Gross!"
by skidmarkymark June 21, 2007
 
2.
a warning from guys to their guy friends when they see them talking to a girl who seems promiscuous or is a well-known slut, to keep them away from said girl, in reference to the girls vagina resembling an Arby's roast beef sandwich.
Sonny: "Hey, dude, I'm talking to that one Megan chick. She seems nice."
Hayden: "Dude, she's slept with so many guys. I'm thinkin' arby's."
by sonnyreyes July 12, 2008