Get out of my galley.I think you have handle the situation good to a point.I would have avoided to confront the pax the way you did by mirrowing his behavior(getting more angry).You became then sarcastic with the reply you gave to the passenger and you dont gain respect from a passenger being in that way.By being short and firm will be better then to back chat.Thats why you got the comment from the pax wife.
''Sir, just a reminder for you, the Captain is in command of this aircraft, not yourself ''
I would have avoided the situation by contacting the captain immediatly and ask if its safe for the pax to use the toilets.If he said no I would have gone back and said ''Sir I am afraid the captain have informed me that is to dangerous to use the toilets could you hang on for a minute?''The pax can then see you did try and help him but the comands come from the captain and he needs to obey by it. I have been in a situation when I was a passenger and it was bumpy and I needed the toilet.I told the crew if they can ask the captain if I can you the toilets and will be quick.They asked the captain and the captain gave permission to use it quick.
The other sentence i read from your post suggest to me you are not open to feedback wich mean you are not an active listener.
''For those of you who feel that I could have handled the situation better, I am an experienced crew member and this is the first time in all the years I have been flying that the seat belts signs have become so confrontational. The man was a complete arse who felt due to "his weekly experience" of flying that route that he knew more than the cabin crew and that he was in charge, even though he wasn't in charge and was not at all aware of the weather situation.''
I have been flying for 7 years and i still learn from this job.Its good to see how crew handle situations and learn from it so when it happens to you you know how to deal it to the best of your abilities.I hope we all learn from it and sometimes put ourself in pax situation.