When he's perfectly capable of doing it himself?
He went to the loo upstairs while I was making dinner and looking after my 20 mo. He shouted for me to - ahem - clean him up - which i did, then I put some water in the sink for him to wash his hands and set off downstairs to rescue dinner and make sure ds2 was ok. When I got to the bottom of the stairs he shouted to me to roll up his sleeves. I said no - you know how to do that. He proceeded to have a 25 minute hit the roof ear splitting tantrum.
Yes it would have been easy to roll up his sleeves but we are having a bit of a power struggle at present and it's just one of the games he plays. What would you have done?