How about someone who leaves the tea bag in the mug, sometimes for multiple days? Sips the tea with multiple bags still in it? It creeps me out and I am not even a big tea drinker.
i had a co worker - who i assume didn't want others to use his mug - who had a special day each year for washing his tea mug. It was soooo gnarly and crusty the rest of the year, he would gleefully take the clean mug around the office and show everyone on cleaning day. weird dude!
I once had a colleague who would get hysteric when someone would clean the coffee machine. People are weird. Not cleaning tea potts and even mugs is also quite common among elder germans. They argue it tastes better that way. (They drink the tea without sugar or milk, so it probably isn't thaaat bad.)
I've done that a few times. Mostly when the previous bag was used the night before, and I was super sleepy in the morning, so didn't even bother ditching it, saving 1.3 seconds and thinking it would make my new tea stronger.
...yeah, I don't do that anymore. But this is why I used to.
UPDATE: I just made my tea just the regular way this morning. While stirring, I realised I had left the previous night's red berry tea bag in it. I didn't want to waste an otherwise perfectly fine bag of Earl Grey, so I did it again. Not intentionally, though.
Also, note to self: red berry Earl Grey is not great.