The comic didn't make it's point well, but to be fair Buffy did have a few instances of vampires being staked with pencils. One of which was wielded by the decidedly not superpowered Dawn.
Personally, I think for staking a vampire in combat to be exciting, it has to be hard. If your average first level warrior can walk up to a vampire and stake it in the heart, vampires aren't going to be scary - and staking one like this won't be an achievement. This is from a storytelling POV separate from the question of whether a that warrior realistically would be able to drive a stake through a normal person's breastbone.
Now, PF actually has a called-shots mechanic that I just found, albeit as an optional variant. A shot to the heart takes a -10 penalty. A basic vampire has at least a +2 Dex bonus, +1 dodge bonus, and +6 natural armour, for a naked AC of 19. An attack roll of at least 29 is necessary to stake one in the heart (and potentially much higher if they're wearing protective items). So that's plain impossible without at least +9 to hit - unlikely unless you're a mid to high level martial.
If the hit isn't either a critical hit or a debilitating blow, the attempt fails and is just a normal hit.
So you can't auto-succeed on your called shot on a Nat 20; if you don't confirm, there's no effect.
And OH LOOK
A critical hit to the heart against a vampire made with a piercing weapon composed entirely of wood leaves the vampire impaled through the heart by the weapon if it fails its Fortitude save.
(earlier: Saving Throws: If a saving throw is allowed on a called shot, the DC is equal to the Armor Class hit by the attack. In the case of an attack roll of a natural 20, the DC is the AC the attack would have hit if 20s did not automatically hit.)
So, to stake a vampire, you can either grapple like a boss, be a crit-fisher preferably with an ironwood rapier, or be a decent fighter and get lucky.