 If you liked
Heppoko Jikken Animation Excel♥Saga
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 ...then you might like
Detroit Metal City
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They both have the same style of "in your face" humour, and both main characters have inexplicable motivations (why does Negishi keep singing for DMC? / how the fu*K did Excel end up working for Ilpalazzo?)
Similar humour, chaotic, not caring a bit for logic or common sense. In both those animes, you can sense how much fun people had making it, and how they likely had few restrictions as to what they could do.
Watching Detroit Metal City reminded me instantly of the unbridled, laid-back laughter I had watching Excel saga.