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1.
Any sexual action, bar none. When you're doing something sexual, your skin by definition has to be touching your own skin or someone elses.
Jacking off? Skin on skin
Fucking a chick? Skin on skin
Fucking a diseased monkey up the ass thereby spreading aids from primates to humans? Yes, skin on skin
by Indigga007 January 02, 2010
 
2.
use of a condom to prevent pregnancy and disease
skin on skin or else I dont go in
by GeorgeSmith August 31, 2007