Is it normal to grass to the manager
I recently caught a colleague rubbing the rim of a 1 pint of milk that belonged to my manager with the end of his penis and placing it back in the fridge in the rest area kitchen, which in turn was laughed off by the rest of the group as a bit of fun when I brought it up and that other things are done all the time to his milk and placed back for him to use, I feel uncomfortable with this as it seems everybody is in on it and I worry about the consequences, as half the people I work with come across as dimwits and are off my level. I want to tell my manager the but I don't want to be seen as a grass or ass-licker while my working days become a misery and isolated.