Teleporting into someone else?

[Neowulf]

what are the rules if you teleport into someone else? I can't find those rules

[MilleniaAntares]

Typically, you can't.

[Neowulf]

what if they're a size or more bigger than me

[Ruethgar]

Still can't. It could be possible if they have a space within them that isn't a part of them(Sculpt Self for a Hole of Hiding as an example though that would also require it be a Transdimensional spell). Also it might be allowed for Intelligent Items of sufficient size like an airship.

[Necroticplague]

what if they're a size or more bigger than me

Irrelevant.

A creature or object brought into being or transported to your location by a conjuration spell cannot appear inside another creature or object, nor can it appear floating in an empty space. It must arrive in an open location on a surface capable of supporting it.

The creature or object must appear within the spell’s range, but it does not have to remain within the range.
Very explicit that you can't do this.

[Erit]

If we're talking 3.5 here, the closest you can get is the Blood Magus' Bloodwalk ability to my knowledge. And even with that, you don't teleport to inside a creature; you just leap into one person's blood and out of another's, with the option of making your exit particularly messy.

[Segev]

Yeah, what you're asking doesn't happen by the rules.

What precisely are you trying to do, and why? Maybe we can help you figure out an alternative.