I haven't IRL (though I believe I may have been in the same building at the same event as Mr. Repzion years ago before I knew he existed.) And also several lolcows live in the same city I do so theoretically I could have passed them and not even realized it as well.
As for actually having talked to cows in some threads on here, not necessarily where there were even a topic of discussion necessarily, though many were. (A Fat Chance, Tommy Tooter, Autphag, Mikemikev, and Oliver Smith)
And then on twitter there's been Zinnia Jones, @Field Marshal Crappenberg (who seems to enjoy pestering me with his latest escapades), Matt/Michelle Perez (who blocked me after one tweet), Hendrik Verbraeken (who occasionally sends me tweets for no discernible reason).
And that's all I can recount off the top of my head.
I've met pamperchu before (I'm not going to say where). Outside of blues clues pajamas and the diapers he's at the very, very least quiet. I haven't heard of him raping kids or his, predictably enough, Siberian husky dog.
All of these are from Tumblr, but I wouldn't be surprised if I've seen Zach Lawless in at least one place in real life. That face just looks really, really familiar.
martinfinnegan - Was friends with them when I was 14 or 15 (they were 19/20, I think?) because of Bioshock. They blocked me for no reason some time after remaking... it might've been because I was openly "truscum" at the time.
IDCP - I used to follow her because I thought she was ~cool~. Unfollowed after all the drama regarding their hatred of trans men, and I'm 99% sure I've sent them an ask at some point.
Cuteosphere - I still like her art, and she's answered my asks before, so I guess that counts?
the-red-church - Blocked me for asking about David Reimer on a post saying something like "theres no such thing as people forcing their children to become trans". This was in 2014 or 2015, though.
I used to follow aaaa42, wendycorduroy, and DameGreyWulf but never interacted with them.
A friend of mine also had thecybersmith interact with one of their posts... don't know if that counts, though.
Does it count that you wrote a review of a lolcow's comic on another forum (PRoject AFTER) and he made a visit? He wrote Marry Me and ended up making an ass of himself trying to explain stuff. Basically he only made the comic to have it hopefully turned into a movie. I made some comments that the potential romantic couple had no real chemistry (the guy also had no real personality or motives), he relied too much on people reading the comment section for info that should've been in the comic and the lesbian who had a crush on the main female was much more interesting character (and the antagonist had the right to defend himself by hitting her since she was the one attacking and trying to strangle him first). He never really answered by points in the review and got butt-hurt.
I mean, I made a thread on the person I felt was worthy of such, and as it turns out, it somehow got featured for a week (must have been slow). I used my own experiences and the screencaps other people provided because it really didn't matter if you were right or left, gay or straight, mean or nice, everyone disliked this guy. One of the few lolcows I've interacted with off-site, but that's honestly because that's how I found him.
A few before coming here and signing up, primarily back and forths on youtube. Honestly it explained so much about my interactions with them to see and read their threads here afterwards.