Personally, I think that's adorable! At home, I would probably leave it alone. If it's really causing problems with his teacher or elsewhere, though, I think I would have the communication conversation:
Communication consists of three parts:
1. the sender
2. the message
3. the recipient
It is not enough for the sender (you) to know exactly what you are saying, and to say it correctly; you must also consider your audience, and whether they are receiving your message as you intend it to be received. Regardless of the technical correctness and sophistication of your communication as it leaves you, it is a failed communication if the recipient does not receive it intact. So if your objective is to communicate, you have to make adjustments to your audience. If your objective is simply self-expression for its own sake, then by all means use language that is incomprehensible to your listeners, if that's what you want to say! (With due consideration for language that would endanger yourself or unduly hurt others, of course.)
And then, of course, there are just some things that we save for home...