whats a reasonable explanation for my door opening on its own besides GHOSTS

Yeah, you just can't trust those lying ghosts. 

Intuitive consciousness can explain why the door opened; the house wanted the door open for some reason. 

Don't mess with ghosts. If you get a ghost trapped, you know, like in a closet or something, LEAVE HIM TRAPPED!

A faulty latch and a badly fitted door and frame installed out of upright....couple that with someone with Bad Wind and you should be thankful the door tends to swing open unaided.....  :)D 

"I had a door that did that in the winter because of the colder temperature."  The door frame would shrink in the winter time causing the latch to barely engage.  Almost any outside breeze could open the door.

Air pressure, loose doorknob, an animal pushing it. 

not sure

Door hinges being out of plumb.

Demon possession.