Damn... "thanks a bunch" = a sarcastic/ironic version of saying thank you. 
Oh boy, and I often used it to thanks people here on twitter for their comments. 
Sorry!! english is not my first language
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Yeah for me too. I were on a plane once where I asked some if I could pass them and they said "sure, what ever" I thought they where being rude but the person were smiling at the same time, making me super confused
