<human>: Give me the gist of the text in a nutshell

The story goes that my roommates and I leaned water cups against room 406's door so when they opened their door the water spilled making their feet wet.  Anyways, long story short, they managed to avoid such a mess and leaned it up against our door.  Yes, it worked.  Our feet soaked in the pride we set out to achieve.  That night my buddy wanted revenge.  He placed (unused) toilet paper, water bottle container, etc on top of a ramp and leaned it against their door so when they opened their door it fell straight into their room.  [Like this]  

They were not exactly happy to say the least.  We woke up to find [this] on our door.

My buddy (yes, he's a redditor too) retaliated with [this](

So now we're at war unprepared.  We ask for fun, harmless, cheap prank ideas that could be done to the outside of their door.

I know you guys can do it!
<bot>: We're at "war" with another dormroom and so we need prank ideas.  Fun, harmless, cheap prank ideas.