Maybe I'm weird but I'm one of those people who normally goes to the bathroom during boarding.
At somewhere like JFK (my home airport) I don't know how long it'll be from pushback until I'm in the air and able to go. Given I'm usually in F I'll head up once boarding has finished, or the stream of boarding is light. I've had several occasions where it's been more than 2hrs from pushback to being in the air just due to it being early evening rush hour so I'll go as late as possible.