I remember being 9 years old playing some online fps game called "We are the Robots" and someone telling me "Fuck You".
I'm not talking being offended by a post that was directed to a group you are a member of. I mean a direct message / text from someone insulting or threatening you.
1997, during a match of Command & Conquer: Red Alert over dialup. I was the Soviets, my opponent was the Allies. Noticed he'd built alllll his power plants in a tight cluster off on one side of his base. I proceeded to shittalk him in chat to the point where he was incoherently threatening to blow my head off with a shotgun (bonus info: this guy was about 13 years old). He was so busy sperging out he didn't notice I had a nuke ready...
Got called a nigger on /v/ once. Don't remember when or why, but that was the first time.
I don't know if it counts, but some time before that, back when I had a Reddit account, I once used the word "transsexual" instead of "transgender" and got a bunch of sneedees trying to aggressively "educate" me about why that word is outdated and offensive for it.