The tabloids enjoyed doing this to Tony Blair in his time as Prime Minister, as he's actually quite good looking until he reveals his giant man boobs.
Then there's that famous picture of Obama...
A September 2009 issue of Newsweek cover featured a Sarah Palin photo that presented her in a less-than-presidential way. Palin and many Newsweek readers were pissed, one who's comment was published in a later issue of the magazine; he asked whether Newsweek would choose to feature a picture of a shirtless Obama"... and they did exactly this, about 20 pages over.
There is a Boston University hockey fan who goes by "Sasquatch" who fires up the crowd by removing his shirt and dancing to "Iron Man". Of course, one doesn't get the name "Sasquatch" if you have a smooth chest and a six-pack...(link, mercifully pic-free).
At a hockey game? And here I thought the Green Bay Packers' "Bikini Girls" were insane...
Matthew McConaughey hardly ever wears a shirt. Exquisitely mocked by Matt Damon on David Letterman: "Ah, Mr. Soderbergh! Today's scene I think would be a good opportunity for me to take my shirt off." If there weren't already three quotes up top, this would be perfect.
Bear Grylls from Man Vs.Wild finds an excuse to take off his shirt, and sometimes his pants, in just about every single episode, sometimes multiple times per episode. Yes, even in arctic conditions.
MythBusters has indulged in this as well. Every single male MB has appeared stripped to underwear/swimtrunks at least once on the show. (Not counting at least three episodes where Jamie goes shirtless but has pants on.)
DMX would remove his shirt towards the end of his concerts, to the delight of the female fans.
The majority of modern gym classes in your average school will require students to change into a different uniform. While the uniform itself usually has a shirt, the boys will generally be shirtless for at least a little while changing.
Ask Nathan Gunn, American baritone, the very definition of "barihunk". Also, you can try Simon Keenlyside or Rod Gilfry.
In Rio de Janerio, it's very common for guys to go without their shirts. The shirtless guys are very popular at parties and nightclubs and are always surrounded by friends and girls.
During the 18th and 19th centuries when duelling was popular among gentlemen, some of them noticed that your chances of surviving a fight were better if you didn't get shreds of dirty cloth in your sword cuts or bullet wounds, so they would duel shirtless (and in at least one case, nude).