He may be telling the truth. Sausage chasers do exist, and they wear some pretty outrageous stuff. It's attention seeking behavior, roughly on par with showing up for church in a banana hammock.
Violating people's expectations and standards *does* produce a result, and it *does* get people's attention. It's not always positive attention, but when it comes to self-expression that doesn't matter. The kind of person who shows up in attire like this *wants* the eye roll, or the sarcastic remark, or the extended knee-on-belly, because it feeds into their need for attention and drama. They like to feel oppressed and judged negatively, so they create situations where people will do that to them.
It's not a matter of offending people, really: it's a question of deliberately attracting attention, especially sexual attention, at a time and place where people are supposed to be concentrating on something else.
There's a time and a place for attention seeking: at a singles bar, at the beach, or on certain Web sites. But there are also places it's not appropriate, because it detracts from the purpose for which people are coming together. At the office, people are there to work. At church, they're there to worship. At the gym, they're there to train.
Trolling for sex in the gym is inappropriate, but a few gear manufacturers have realized there are enough people who want to do it to create a market. So they're catering to the inappropriate behavior and enabling it.
The fact that someone caters to, or enables, an inappropriate behavior doesn't legitimize the behavior or make it acceptable.