WIBU unreasonable over the washing up

[issano]

Ok I'm going to explain this in terms of person A and person B.
Generally on weeknights person A cooks and person B washes up. The last two nights person B has been busy so person A has both cooked and washed up (which is fine).
Last night person A decided to wash up whilst cooking tea (so all the mugs/plates/bowls etc used since the night before) as tea was only shock horror chip butties, so only one baking tray and 2 plates were being used.
Therefore after tea person A didn't wash up again as thought it was a waste of water to run a fresh bowl.
This morning person B has noted that there are 2 plates, a baking tray, and 2 mugs that haven't been washed. Person A explained there was no point running a fresh bowl of water.
Person B is not happy and said that as they are chief washer upper it should be done how they like it. Person A has said that if they are that bothered they are happy for person B to leave 5 items of things to wash up tonight and they will do them, to which B replied they won't be doing the washing up at all (even though person A is busy tonight and will be rushed enough cooking tea).
So WIBU unreasonable A or B?

person a should tonight get themselves a take away pizza, eat said pizza and put box in bin, dealing both with their dinner and washjing up at same time...person b can carry on with what they want to do, that kept them so busy they couldnt do their job even though it was only wash two mugs and two plates, they managed to find time to eat out of and drink from.

Wash up and put the little bit away, then don't cook, grab something on the way home.