How do you feel about saying thank you, and being thanked?

I cop a lot of shit for apparently being thankless, meaning when somebody does something for me or gives me something, I come across as ungrateful. But when I give stuff away, I never even expect a thank you... Shit just seems meaningless to me. Its not that I dont feel grateful, I just think it isn't necessary. And thank you's often seem insincere anyway, so I feel like im demeaning their good deed by saying meaningless words, yet they expect it.

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