What are some good shampoo pranks?

I think my roommates are using my shampoos, since whenever I come home to shower, there tends to be less shampoo in the bottles than the last time I used it. Is there a way to tell if someone is using my shampoos or not? Realistic answers please, don't google a bunch of pranks and spam them on here. 10 Pts to the best answer !What are some good shampoo pranks?
1) Empty the real shampoo.





2) take the '; hair removing cream, bleach, Dog Shampoo, and few grams of salt ( Sodium chloride ) or baking powder ( Sodium bicarbonate ) ';





3) mix the contents well, hey dont leak the plan to any of your friends.





4) Dont expose your trick by smiling all the time, be normal.





5) let them have the bath first.





6) Wait and watch, Enjoy the fun.





I hav tried it on my bully, but he turned into a baldy.What are some good shampoo pranks?
Empty the shampoo into another container(and hide that)and put some liquid that when used you can see easily(without them able to wash it out in 3 days)Or shampoo for girls that smells all girly, and that you can sniff and see.
You could always put a different type of shampoo that has a strong scent and sniff them after, haha. (I'm being serious, some shampoo scents can be smelt across rooms. *shudder*)


Or, you could put hair dye into the bottle. Or food colouring.


Cover a small section of the shampoo bottle in whiteboard marker. (It'll be rubbed out where they've handled it without noticing)


Ask them if they've been using it.
ask them - they say no - put dye in it :D
put bleach in it

white makeup