Hi Pickle, As it was you who saw it, it may be best if you sit down with for a friendly chat as to what you saw and just how its no good for him, some how it needs to be done in a seious but real friendly way, if you get my picture.
Good Luck
Well depending how old you are you can talk to him and tell him that it is not apple juice (kid probably thinks it is because of the color). You can also tell his parents. It's not something that is horrible, he is a kid and is mistaken about something.