If they're a:

Medievalist - turn off the light every time they enter the room and turn it back on once they leave.
Cartesian - hum the ghostbusters theme whenever they are around.
Spinozist - copy all their actions in parallel.
Idealist - stare at your victim intently for a few minutes then close your eyes and mutter "you don't exist you don't exist you don't exist", then open your eyes and look really disappointed that God kept your victim in existence.
Humean - throw things at them and when they look at you accusingly deny that you were the cause.
Kantian - rub their desk with rosin. When they ask what you're doing say "I'm making sure your desk conforms to the principles of pure resin!"
Fregean - challenge them to complete a 1000 piece puzzle. Don't tell them it has pieces missing, they'll only be able to complete it in a sense.
Millian - glue 3 pebbles to their desk and challenge them to prove that 2 + 1 = 3
Russelian - start carrying around a 'denoting' stick and whenever you say their name poke them with the stick.
Essentialist - chip off a bit of their desk and then claim it as your own since it is no longer the same desk it was before.
Logician - make some angled brackets out of cardboard and try to contain them in a set with yourself OR stick a negation sign on their back.

I may illustrate some of these eventually...

Other suggestions for pranks are welcome!