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Wah-wah sucks.
I totally hate it. The only time I can stomach it is when J Mascis steps onto it and thrashes his guitar so it goes "WAAAAAAAAAHHHHHHRRRRRRRRAAAAAAASSSSSSSSSHHHHHHAAAAAAAAAAAAAHHHHHHHHH!!!!!!!!" So much better than that Clapton "wah-wah, wah-wah, waaaah" bit of wank.
What guitar effects do YOU hate?