An astounding ability some people possess that makes them seemingly invulnerable to virtually anything thrown at them.

An important side note: invulnerability only lasts so long as the sufferer of AHS does not need to be around, is somehow expendable, or is otherwise unimportant. They can do anything until it really matters.

Famous sufferers of AHS are: the GOP, Micheal Jordan's career, Any transvestsite dates, And veritably any protagonist in any action movie made in any date of modern history.

This can be easily applied to any every-day scenario, though is usually left to more unbelievable acts.
Jerry: Man, I went driving with Skippy the other night, and he sparked a bowl right at a stoplight!

Chris: you get caught?

Jerry: No, even though a cop pulled up right behind us! he's, got, like Action Hero Syndrome, man!

or

Larry: Wow, seriously? He got arrested for smoking weed?

Nick: Yeah. He decided that it was a smart idea to light up right in front of the police station.

Larry: How is it that the one time he gets caught, we're waiting on the porch of his house to let us in for the party? It's raining!

Nick: I don't know what to say, man, he's got AHS.
by F1g_N3wton June 5, 2009
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The tendency of many macho guys to brush off pain from serious injuries in day-to-day life, while behaving like complete blubbering weenies when receiving routine medical care. This allows them to appear to have a (manly) high pain threshold, and yet still get copious sympathy from loved ones at the hospital.
Jenna's husband didn't flinch when he sliced his hand open while renovating their kitchen. But he sobbed inconsolably when they put in an IV at the ER. Jenna coddled him and yelled at the nurse, but it was a clear case of Action Hero Pain Syndrome.
by Sir Elroy May 11, 2011
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