To be deliberately, aggressively, irrationally stupid. Similar to how people who are addicted to Oxycontin/oxycodone/painkillers behave.
I saw John steal $20 out of my wallet. When I confronted him he said fuck you and I had lost the money somewhere else. Totally oxytarded. (or) What an oxytard.
When you fail at something in life (eg. failing an exam or not getting a job), go home and spend an hour just standing in the shower, propping yourself up against the wall with your eyes on your feet.
Caleb knew the only thing to do after he didnt get prefect was take a failure shower.