Even the least douchey of bros knows that you look your most pumped right after a workout. Every frat dude in the country will tell you that the gym mirror is the perfect place to snap a selfie after you've pumped that iron and downed the day's peanut butter and creatine smoothie. Don't stop at simply snapping a photo in front of the weight rack mirror, take a series of selfies on every single piece of equipment until your find the most flattering pose for your profile picture. Some figures are best flattered by weight belts and squat racks while others look best mid-cable curl. Granted, you might annoy people who actually come to the gym for a serious workout, but there are so few of these types of people out there that this shouldn't present much of a problem.
Take pics at the gym.