I think this works, but I wanted to get more opinions. Before combat starts, say you're talking in a bar or walking down the street. Can you Quick Draw a dagger and use Deft Palm to hide it from people next to you? As long as your Sleight of Hand check beats their Perception of course.
Deft Palm: " A rogue with this talent can make a Sleight of Hand check to conceal a weapon while holding it in plain sight, even while she is being observed."
I would then combine that with other Rogue talents such as Betrayer, Quick Shot, and Underhanded.
Betrayer: "When you succeed at a Diplomacy check to change a creature’s attitude, you can draw a weapon and make a single melee attack against that creature as an immediate action. If you changed your target’s attitude to friendly or better, your target is considered flat-footed against this attack"
Quick Shot: "Whenever the rogue rolls initiative, she can also make a single attack with a ranged weapon as a swift action. She can use this ability only if she has a weapon in hand and it is loaded (if applicable). If more than one rogue has this talent, their initiative check results determine the order in which they make their attacks. After these attacks are resolved, the round proceeds as normal."
Underhanded: " A rogue with this talent gains a +4 circumstance bonus on all Sleight of Hand checks made to conceal a weapon. Furthermore, if she makes a sneak attack during the surprise round using a concealed weapon that her opponent didn’t know about, she does not have to roll sneak attack damage, and the sneak attack deals maximum damage. A rogue can only use the underhanded talent a number of times per day equal to her Charisma modifier"
So BEFORE anyone takes a turn in the surprise round, I've already made 2 Sneak Attacks against my target. Betrayer lets me draw a weapon and attack, and I already had a dagger concealed in my hand with Deft Palm which Quick Shot lets me throw. Underhanded gives me +4 to Sleight of Hand with Deft Palm, and I do max sneak attack damage. Anything I'm missing about why all those wouldn't work together?
Well, let's walk through it.
1. You quickdraw a dagger. Fine so far. You use Deft Palm to hide it from others as a standard action via sleight of hand.
First fail point is in being spotted in this action. Assuming no one notices and/or screams, continue on.
2. You attempt a diplomacy check to change a creature's attitude. Second fail point. Diplomacy takes a minute which may mean more perception checks against your dagger (dm dependent). Additionally, you MUST succeed on the check to activate betrayer. If you succeed you can draw a weapon and make a melee attack as an immediate action. They may or may not be flat-footed to it depending on your diplo results, so sneak attack may or may not apply. So if your dagger has been spotted, or you fail the diplo check, the combo fails. Let's assume neither of those things happen and continue on. You draw a second dagger with your other hand, your attack hits, you deal damage, and the dm calls for initiative.
3. You roll initiative and here there's a little weirdness depending on how your gm wants to do things. In part 2, you used an immediate action to draw a weapon and attack. Technically, it is not your turn when you do that since initiative had not yet begun, which means you technically can't use another swift or immediate action until after your next turn. However, I think most gm's wouldn't care specifically because it happened outside of combat. But it is a potential fail point. Continuing on, you now use a swift action to throw the dagger you drew in 2 at your target. If your target is flat-footed (doesn't have uncanny dodge or similar) you can deal sneak attack damage. However, you may also suffer an attack of opportunity if they have combat reflexes. Ranged attacks provoke and you're definitely within range.
4. Finally, we get to underhanded. This only works during the surprise round AND only if you can deal sneak attack damage. That means winning initiative and your opponent not having something that would negate it, like uncanny dodge.
In short, there is one potential gm fail point involving the action use for quick shot and underhanded.
Assuming your gm allows those to work together the combo can work. Though there are a number of spots that 'derail' parts of the combo.
Honestly though, I think the biggest difficulty with this combo will be how often you end up using it. I wouldn't think you'd have many occasions where you'd want to kill someone AND they'd be willing to let you walk along next to them while holding a conversation.