1/2 phase 1/2 habit.
The "Do it mySELF" part is a phase. The words he's choosing are pushing boundaries/habit.
I'd recommend a flanking option. AKA make him think/feel all independant, when he's actually learning to use his manners.
1) Give him some freedom where appropriate / WITH boundaries. For example some options are:
- Giving him HIS shelf on the fridge. Keep his sippy/juice or milk boxes, and approved "anytime" snacks. Grapes, goldfish, yogurt, leftovers from lunch/bfast, whatever. We used a shelf on the door, because it's at eye level and it's SMALL.
- Clothes choices
- Timers (aka, I'm going to set the timer for 5 minutes. After that I'm going to help you. If you can get it done before that though, you can do it yourself.)
- Etc.
2) Word Choices
- ASKING first. Get that habit ground in. Even for HIS shelf (if you do that), he may only have or do something IF he asks and asks NICELY. "Put it back, you forgot to ask" will probably be a phrase that falls out of your mouth a lot the next month. Then when he asks, the answer is yes. As many times as you possibly can. Get that whole positive reinforcement going. "Of course you can sweetheart, since you asked so nicely". The other phrase is correcting tone "Try again, nicely this time".
- Being rude is hitting without using your hands. Repeat THAT phrase about a gazillion times, and use the same punishment you use for hitting.
- "Only if you will __________." aka let me help you, don't drag it, ask nicely, can do it by the time the timer goes off... add in those qualifiers!!!
Anyhow... just some ideas from what we've done in our house.