I think it depends on what sort of establishment we're talking about here. Bathouses and saunas, of course it's okay and expected to see things like cockrings and boners. Locker rooms in gyms that are known to cater to gay men looking to cruise... yeah, okay. But a public gym where the general public goes to work out, including families.... in that case, I think wearing a metal ring on your dick that's designed to produce erections is weird and inappropriate. Call me a prude....