Not recognizing somebody I've known for years because they have done something to their appearance like cut or dye their hair, get older, change their weight, or are in an unfamiliar environment (e.g., I see a client at the theater). It's like they look like a whole new person.
I used to have a co-worker that could do the most astounding, gorgeous things with her hair. Every two or three Mondays, she would come in with hair extensions, braids, coils, dyed hair, up-puffs, or short hair. It was like she'd had a head transplant. It was so damned embarrassing to be thinking, "Ummm, I think that's J--. I've only known her for TWO YEARS." Fortunately I was pretty good at recognizing voices. I was terrified she'd figure it out and think I didn't recognize her because she's African American, but I am an equal opportunity clueless person. I can fail to recognize people of any ethnicity.
If I ran into a client I hadn't seen in several months, they'd be chatting away at me for a while, and I'm hoping that they will drop some hint as to what project we worked on. If they start off with a sentence like, "You remember that booklet you did for me last year," I panic! Which booklet? I've done lots! Who the hell are you??
I think one of them caught on, because the last time I saw him, he told me his name, even though I do a lot of work for him (mostly over email instead of face-to-face).
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Diagnosed Bipolar II in 2012, Autism spectrum disorder (moderate) & ADHD in 2015.