That's Crazy
The perfect response when you haven't been listening at all; it works whether the other person has been saying something funny, sad, infuriating, or boring.
Guy 1: My Girlfriend dumped me last night.
Guy 2: (not paying attention): Oh man, that's crazy.
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Don't even pretend you have never used this. I tend to revert to this when someone gets monotonous or redundant on me. It's not my fault that ppl decide to ramble to me when I'm busy! D: (*is referring to actual convos, not net convos. For those I just brb*)