i m pretty sure that this prank will work because toothpaste is something which one uses in morning or evening and at that time one feels sleepy ...so thus your mission will be completed
personal note-i experimented it on me and trust me it will fire up your whole mouth///
Materials required are chilly powder and toothpaste ......
so after you have got all that stuff u need to fill chill powder in the toothpaste
this is the most important step mix the chilly powder well so that victim should have no doubt on colour difference
next important step is that clean the extra chiili powder from the tube so that victim should have no doubt
put the toothpaste back in place and you are ready to go...