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1.
According to the legend on Andy. Ninjahoppin is the act of spying on people in your neighborhood at night while wearing black clothes. To catch them masturbating of having sex.
Andy and Scott went ninjahoppin' late at night to spy on some fools.
by guywargamer May 30, 2005
 
2.
Ninja Hoppin is when you go from house to house looking in people's windows like peeping toms, but when you find a couple having sex, be it strait or gay, you sneek up on them and join them, it ends up as a threeway gangbang.
you guys have fun ninja hoppin yesterday, cuz i sure did, I found 3 houses in one night.
by Sodapop April 03, 2006