I gotta go with Krist Novoselic. He would throw his guitar up in the air- and (usually) catch it. The lion's share of people hear with their eyes, and his stage presence and energy were pivotal in Nirvana's performance. He also executed one of bass guitar's most important lessons: amazing tone. Given Nirvana's impact, from here on out more and more future bass players will be influenced by his work.
/fanboyanalysis
Jaco did that too. Just sayin'...
Anyway, I'm going to go for John Deacon from Queen. He and Brian May always had this calm, cool look about them. And the guy from the Living End- not sure of his name, but he plays upright, and would lean it so the bottom left corner was touching the ground, then jump on the side of the bass and keep playing. Probably not very good for the bass, though...
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And there you have it.