According to this heavy-duty etymological research, asshat wasn’t used on the Dope until August, 2001, and was spotted on the Usenet in 1998.
The OED hasn’t returned my calls.
“Asshat” is big on TWoP (Television Without Pity) too. Actually, so is claiming everything as a shout-out. I wonder who originated that? 
I’ll be convinced when I finally hear “penis ensues”. Kent Brockman had half of it once*, come on Kent, go all the way**!
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- How do you know we’re live? PENIS!
** - no, I’m not saying he got “penis” from here. He got it from his pants.
C’mon, the zombie was laid to rest today!
Christ. I used to be on another message board that also thought it invented “asshat.”
When will this asshattery end?!!
now here I was all ready to post my favorite alternate to the regular asshat that I have never heard another soul utter in text or in real life and here some basterd on the dope beats me to it. 
seriously you should try asking “What the HELL kind of Asshattery is GOING ON in here?” sometime. it just feels right.
I am SICK and TIRED of these MOTHERFUCKING ASSHATS on this MOTHERFUCKING MESSAGEBOARD!
Wait . . . what? We didn’t invent that either? What about “plane onna treadmill”? “14 k of g in a f p d”? Hmph. Fine. But you can have my manny peoples when you pry it from my cold dead hands.
FWIW: 1976, in the movie The Outlaw Josie Wales, a Union officer threatens the kid Jamie with: “Now get back in line, boy before I kick you so hard, you’ll be wearing your ass for a hat.”
Burr and Hamilton faught a duel over which one had originated “Asshat,” and whether it looked like “Affhat.”
Just in case no one has pointed this out yet, Asshat did not originate on the SDMB.
Also, That 70’s Show debuted in 1998.
So that means it dates back to the Civil War at least, right?