The real shampoo prank!
Practical jokes differ from confidence tricks or hoaxes in that the victim finds out, or is let in on the joke, rather than being talked into handing over money or other valuables. Practical jokes are generally lighthearted and without lasting impact; their purpose is to make the victim feel humbled or foolish, but not victimized or humiliated. However, practical jokes performed with cruelty can constitute bullying, whose intent is to harass or exclude rather than reinforce social bonds through ritual humbling.
A practical joke is a mischievous trick played on someone, generally causing the victim to experience embarrassment, perplexity, confusion or discomfort. A person who performs a practical joke is called a practical joker. Other terms for practical jokes include prank, gag, jape, or shenanigan. (source : wikipedia