To the best of my understanding, it depends on if you're throwing it at them as a active threat, or as a roleplaying encounter. If it's a straight RP encounter:
Pure roleplaying encounters generally have a CR equal to the average level of the party (although particularly easy or difficult roleplaying encounters might be one higher or lower).
If it's something actually attacking them in a way that poses a real obstacle, then it's an obstacle/monster they need to overcome, and so it's rewarded according to the encounter's CR:
Keep a list of the CRs of all the monsters, traps, obstacles, and roleplaying encounters the PCs overcome. At the end of each session, award XP to each PC that participated. Each monster, trap, and obstacle awards a set amount of XP, as determined by its CR, regardless of the level of the party in relation to the challenge
If it's a RP encounter they provoke into becoming a threat and then escape, you could rule either way. I'd probably treat it as an RP encounter.
All quotes: http://paizo.com/pathfinderRPG/prd/gamemastering.html#_awarding-experience
Thank you! That helps.
I can't remember what thing I was reading, and a random encounter had a Hill Giant. Nearly impossible for the party to defeat, but there was some way to get the Giant to leave them alone, so would you reward then party 3,200xp? Or is there a different CR level the party should receive?
I would consider that a RP encounter, so the XP would be determined by finding the CR equal to their APL.
eta: Unless the giant was attacking them rather than just hanging around, in which case it would be 3200
I would say if they negotiate their way through it, full xp (maybe even a bonus).
It would really depend on how dangerous the situation was, overall. Befriending a friendly ancient gold dragon should not give a level 1 party 300,000XP.