A sly five is essentially a high five, but can only be used appropriatly when somebody has accomplished something very sly.
Two kids at school steal a friends pencil case with out him noticing.

Kid 1#:wow, your really sly at stealing things
Kid 2#:this calls for a sly five

Two assassins kill their target from one thousand feet away using a silenced sniper rifle. Nobody notices.
Assassin 1#: omfg that was awesome
Assassin 2#: sly five me
by jedimasterjames January 14, 2010
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A sly five is something you do when you and/or a friend both notice (or do) something awesome in the presence of a person that might not think it awesome. It is essentially a very discreet high five which requires no elevation of the hands and can be done with a simple pass so that no one will notice how awesome you and your friend are.
John, Steve and Rebecca(John's GF) are at the bar with some friends. One of their friends, Elaine, has been hinting at some sexual tension between her and John. Shes awfully drunk now and starts to grope on John when Rebecca isnt paying attention. Seeing the obvious possible confrontation, Steve swoops in and entices Elaine to go and smoke with him so that John and Rebecca can quickly leave. On their way out, John quickly Sly Fives Steve.
by Cohlt .45 May 21, 2010
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Semen spit into a blowjob giver's hand and used to high five the blowjob receiver. To be used when blow job receiver refuses to kiss blowjob giver because his splooge was in his partner's mouth.
My boyfriend refuses to kiss me after I give him blowjobs, so the other day I gave him a sly-five.
by Glockstar January 17, 2016
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