If the person you are giving the secret handshake to isn't privy to it, don't do it.
I was at a Halloween party last night with a friend of mine when someone said something to where we both had the same hysterical reply. This little coincidence warranted a high five. Well, we got the high five in and I was done. Apparently he was going for a secret handshake/high five that I wasn't aware of beacause I put my hand down, looked over and the scantily clad young lady sitting next to me when BAM!. My forehead got high fived. Seriously, WTF!? I now have a knot on my head from where the inside of his ring connected to my cranium. Hilarity, of course, ensued.