Excessive and jingoistic American patriotism. Believing that America is not just the greatest nation on earth, that those who don't share your rabid, short-sighted, patrio-erotic feelings are traitors and should be deported or shot (preferably both). Toby Keith and his fans are most-often associated with the Amerigasm. People most likely to experience an Amerigasm are those who believe President Bush is the 2nd coming of Christ, who believe the US is infalable, and that any problem can be solved by shooting at it. The previous list of people are most likely to include members of the NRA, the Republican party and viewers of Fox News.
Listening to Toby Keith's song "Courtesy of the Red, White, & Blue (The Angry American)" gave me an Amerigasm.