A Manly Handshake is a special sort of skill challenge than can occur anywhere and at any time. The only prerequisite is that 2 individuals be engaged in a handshake. I will do my best to outline the full breadth of uses for a Manly Handshake.
Handshake: Free action, requires at least 1 free hand each (You must have a thumb on your hand), handshakes require full consent from both parties or a successful unarmed attack vs. the target's Reflex defense.
Manly Handshake: Minor action: Requires you to be engaged in a handshake. Make a Strength attack vs. the target's Fortitude Defense. On a success, you are conferred a +2 bonus on your next Diplomacy, Bluff, or Intimidate attempt against the target. On a failure the handshake procedes as normal. Special: On a critical hit, target falls prone and asks you to please let go.
Turnabout Handshake: Immediate Reaction, Free action, Trigger: A creature attempts a Manly Handshake against you. Effect: Roll your own Manly Handshake against the target. On a success, you negate the success of your opponent's handshake. On a failure, your opponent gains an additonal +1 bonus to their next Diplomacy, Bluff, or Intimidate attempt against you. Special: On a critical hit, target falls prone and asks you to please let go.
If you use Turnabout Handshake to negate your oppenents success, you may make your own Manly Handshake as an opportunity attack, gaining any relevant bonuses to opportunity attacks you may have.
Both players may continue to attempt to out-Manly Handshake one another in recurring rounds, though for every 2 rounds that pass, both will lose 1 healing surge due to the sheer exertion involved.
Once 8 rounds have passed, any nearby character can, as an immediate interrupt, suggest that the creatures involved in the Manly Handshake are holding hands, in which case either handshaker can end the handshake without suffering any failure effects.
And an important note: If you have Melee Training (Any), you may substitute the attribute associated with your Melee Training for your Manly Handshake attack.
Another important note: Monks may use their proficiency bonus from unarmed strikes for their Manly Handshake attacks as well as any applicable enhancement bonuses.
Racial Modifiers: The following races have a +1 to any Manly Handshake attempts: Dwarves, Half-Orcs, Goliaths, Warforged and Shifters.