This prank will aggravate them four-fold. Firstly, their shampoo bottle will appear blocked, causing them to squeeze it harder. Secondly, it will explode 'shampoo' (actually cornflour and water) all over them. Thirdly, if you carry it off well, they will think they wasted all their shampoo. Especially annoying since shampoo is so expensive! Lastly, if they don't notice it's not quite its normal consistency, they might rub it in their hair!
- sharp knife
- glue gun
- mixing bowl
- empty shampoo/conditioner bottle (must be opaque)
- food colouring (optional)