a person who is oblivious to the fact that they are geeky, nerdy, weenish, fucktardy or dweeby, one who believes themselves "holier than thou", awesome, powerful, but is in reality mediocre at best in every standing of the typical human cluster. In other words, a literal egotistical idiot.
"Woman 1:That guy in customer service is an asshole. He can't tie his shoes but he thinks he knows about proper business management.
Woman 2: No, he's just tardcore."
"Fuckers who act like they know everything about anything, man they be tardcore shitheads."
"Kevin the Sea Cucumber from "Spongebob Squarepants", is a prime example of "tardcore".