Nothing is springing to mind. All the people who I've known in the past and got on well enough with to see again ... I have done. Or at least I've tried and failed. Same as anyone's done on Facebook. There's also an additional rule which I was given verbally and firmly: I can't include any women that I said anything more then Hello to*.
I'm blank. Would the old chap in the library count? I said 'Hello' to him** yesterday (technically 'in my past') and haven't seen him since. A pedant might argue about whether or not I 'knew' him, though, as I'd never seen him before and he didn't look up or reply to my hello. Even though I sensed a connection as we shared that table for ten minutes, I suppose it wouldn't be in the spirit of the challenge.
A quick initial riffle through the people I went to school or university with or have worked or shared a flat with since rules them out. But already a few faces and places I'd forgotten have popped up, and even if most of them made me wince and immediately pop them back down again, that's going to be the value of this challenge – pulling out the mental shoeboxes from under my mental bed and going through them, mentally.
*Actually, an expression was used here which I've only heard once since the early eighties, and which made me blush.
**Not a euphemism. Definitely not the early eighties thing.