I came back from lunch to find my coworker sitting at the kitchen table using my personal tea mug. We all have our own mugs, and we know whose is whose. I lightly said "hey, that's my mug" thinking I'd poke her a bit but I wasn't really mad. Yet. Until she said:
"Oh I know, but it's the biggest and I wanted to fill it all the way up with bone broth"
She filled my tea-only mug with disgusting collagen-y bone broth and heated it until boiling in the microwave. She clearly knew from my expression that this was not okay and hastily offered to handwash it to make sure it didn't stain or leave a film, but AIBU to be really pissed off? Who does that? Use your own cup and fill it twice, but don't ruin mine! Because it may be ridiculous but I feel like my lovely favorite mug is ruined for tea.