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1.
Japanese for flat chest.
And probably one of the most addictive songs in the world.
(weeaboo1): THAT GIRL IS SO KAWAAAAAAAAAAAAAIIIIIIIIII!!! (^-^)
(weeaboo2): HAI, BUT SHES A TSURUPETTAN
(^-^)
a few seconds of silence...
(weeaboo1 and 2): KAWAAAAAAAAAIIIIIIII!!!!!
by godday to you sir. Whats that? November 01, 2008
 
2.
Actually it means "flat and smooth"

Pettan alone means flat. For example, the suffix -ko means "girl" (such as in meganeko, megane = glasses so glasses girl) so pettanko means a flat (chested) girl.

Tsuru means smooth. So smooth+flat.
Pettan, pettan, tsurupettan! = Flat, flat, smooth and flat!
by tyciol April 10, 2011