I own an Assos bib and the strap unhooks in the front. However, I still have to take everything off to go to the bathroom because it's nearly impossible to get the top part of the short over your head and back again under your jersey - so if you consider buying one for the comfort of not having to bare yourself completely, it's not a good choice.

I don't know if there maybe is a model that unhooks in the back too. That would be a different story.