2 moments!!
the first one was watching smug alert as a kid. i hated Cartman up to that point. always getting on Kyle's case, always trying to hurt him or kill him. hated that guy. so the reveal that he didn't actually hate Kyle but enjoyed his company hit me like a cold bucket of water...the dramatic lighting when Cartman saves Kyle, I remember thinking 'oh shit, this is serious'. and then his little smile after getting Kyle back and resuming their regular dynamic...I was a kid, I didn't do shipping...but it did something to me for sure...something I would later in life understand...
the second one was a few years back and what dragged me back into the fandom. I was tired of seeing people online rag on South Park (lol) so I picked a random ep to confirm I still loved the show. Fate had it be 'It's a jersey thing' and I was reminded of how funny I found Cartman and Kyle's dynamic. But when Kyle turned into Kyley-B (against his will) to save Cartman, I felt a cold chill down my spine. I was like oh no, oh no I can't be doing this now....but then fucking Cartman had to pinch Kyle's cheek and call him his little monster and it was sealed for me. I felt the call of OTP