My girl has a female friend who we do stuff w/ about 7 - 10x a year. Her brother is always there.
He is a tall skinny, pimply ginger with an Asian girlfriend. Memorable enough.
Before he dated the Asian, he dated this loon who would mix her meds with booze.
One night she was freaking out and wailing so loud the cops had to be called to the party. I LITERALLY caught her as she jumped out of the guest bathroom window right before the cops arrived.
To this day (after maybe 50+ meetings), the ginger will still come up to me and my girl, squint, kinda point and say "Yeah, I think maybe I met you one time before somewhere... 'sup??, nice to meet you!"
I save people the embarrassment and reintroduce myself if there is even a hint that they have forgotten. It's better for both of us that way. They save face and make it a priority to remember so they don't look bad the next time.