Here's a piece of free advice: Always be nice to anybody who access to your toothbrush.

I worked in a dorm and one year there was a guy who was in his 40’s living in them with the young guys. He was kind of strange, it was his first time ever moving out from his parents but his job did him a favor and gave him a full scholarship so he moved out. Well he would tell me that there was a guy who tried to bully everyone and the rest of them were getting fed up with him threatening & acting tough. He mentioned several times that the bully left a basket with his shower & dental supplies in the shared restroom & anyone could take his toothbrush and dip it in the toilet & he would never know it. I think he did just that. 😂 that guy didn’t seem like the kind of person to do it but he was fed up like everyone else.