Please help me stop my kid playing with soaps

Get him some bath toys and tell him that they are much more fun than playing with soaps.

Define 'misuse'...

Does he eat them, or just plays around with it?

In the first case, I would not give him soap and shampoo any more.
In the second, I would leave him to it!

Or, does this person use the word "misuse" rather than "abuse".

Is the child using the soap for masturbation? If so, is that really what the poster is worried about?

this is what that person meant when s/he said that no one deserves fundamentalist parents.

Put the soaps and shampoos out of reach.

It scares me that a parent of a toddler didn't think of this right off the bat. Not to mention, what is a toddler doing in the bath alone, unsupervised by a parent? If he's supervised, you wouldn't need to worry about his "misuse" of the soap because you'd simply keep him from doing it.

Also, three year olds understand the word no. Have you tried? Kids aren't as dumb as you think.