The thinly veiled threat is a classic. Just make sure you have something to back it up with if you try it on an NPC, because you know the GM is going to call your bluff otherwise.

Transcript

Padmé: I cannot allow my people to be used as food. But I offer myself if you will help save them.
Jar Jar: {aside} Mmmm... Royal jelly.
Obi-Wan: You can't sacrifice yourself. There must be another way.
{beat}
R2-D2: Well?
Obi-Wan: {aside} Unfortunately they probably don't eat metal.
Qui-Gon: Wait!! Do they eat giant fish?
Anakin: Boss Nass, the Gungans can't get to the Trade Federation's orbital headquarters without our help.
Boss Nass: Whysa we caring about that?
Anakin: That's where your Orb is. It'd be a shame if someone's fighters accidentally destroyed it.
Boss Nass: Hmmm.
Boss Nass: When yousa put it that way... Wesa be helping you.
Qui-Gon: Cool. In that case, do you know where the Lost Orb of Phantasmic Opulence is?
Boss Nass: Um. Yes.
Obi-Wan: Seriously, man. Focus.