What should one do if one comes to the realization that one is 'that guy'?

what a fucking cockgobbler
who the fuck does that

People hold grudges and don't forgive. You will never be able to escape the stigma of being "That Guy" to your group. So I suggest you leave as soon as possible and hook up with a new group.

Take some anti testosterone pills Jesus Christ man

kill "one's self"

Proceed to killing other that guys until only one left.

Because Veeky Forums is'nt one being.

I'd react the same

I realized I was That Guy after playing consecutive 3.5 games as a Wizard, DMM:Persist Cloistered Cleric, Druid, Archivist and most other people seemed to be playing more natural "I thought it would be cool" characters the whole time.

The solution was banning myself from Tier 1/2 and also avoiding overly cheesy optimization in lower tiers (uberchargers), and actually playing a weak character with flaws. Our party actually died less since the DM no longer had to play rocket tag with me.