A description given to one who embarks, or plans to embark on a dangerous adventure. This adventure may mean losing their job, friends, or even their life.
Telling friends or family about it will usually elicit accusations of being crazy or suicidal. But they do it anyway, despite these pessimistic notions. After all, the reward is worth all the risk.
Did you hear about Sean? He says he's going to ride a motorcycle to the tip of South America!
Why the hell is he doing that? That guy is adventurcidal.