You have a Mail then you write "**** You :)" in the mail then give the mail to a Pokémon and then trade the Pokémon holding that mail to another person.
Did people already do this or it still happening?
Mail was in Gens 2-5. Of these, only Generation 2 could have people writing profanities in them, due to anything being able to be put in the message. After Gen 3, people were restricted to a list of pre-determined words that they could use, this being called an easy-chat system. This function was expanded on in Gen 4 and 5 with even more restrictions like message structures. So, only Gen 2 had Mail that could include profanities.