Add a listing on Gumtree for ‘Free Beer – due to being out of date’ and insert your mates phone number, place the listing in a large city and boom! Probably against 1 or 2 T&Cs.
Turn everything upside down and if you’ve got the time/glue/tape then stick it to the ceiling
Cups of water filled in a room will take ages to complete but it’s well worth the look on their face
Wrap everything in old newspapers, cling film etc
Seal their door with crap.
Swap Oreo filling with toothpaste (warning: possible Oreos will get wasted so maybe only do 1 or 2, the last ones for added long term fun)
Chuck a load of cress seeds into something they use, top up with water (not always needed). Be sure it won’t f*ck up the product otherwise you will end up paying for it!
Get a balloon, strap it to an old cereal box, cover it in icing and pretend it’s a cake.
Tie Mentos to a diet coke bottle cap and wait for it to drop (very messy so avoid near their valuables etc).
Fill ketchup bottle with baking soda and wait!
Be careful that you don’t f*ck their car up with this one and be ready with a hoover afterwards as they will probably want you to clean it!