Do you want help or are you just ranting?
Mice can get through a hole the size of a pencil. Yes. A Pencil.
Rats can and will chew through walls to get inside.
It could be a mole, rat, mouse...if it's already in your house, propping a chair against the door isn't going to stop it - sorry.
You have several options -
call an exterminator (yes, I know your land lord is out of town and he's responsible but do you really want this thing crawling into your pots and pans?)
go to home depot or lowes and purchase a can of insulation spray and spray it where you think it (and please keep in mind they usually have a scout and bring the rest....like ants) is coming/getting it.
go to home depot or lowes and purchase a trap.
Not a gigantic beast with fangs - but a rodent with a ton of germs!!!