I'm undiagnosed but I can relate to this post so I'll answer.

I also dislike being told to do things. A lot of times its something that I completely forgot about (ex. left half eaten food with dirty dishes on the table and went to read for an hour/ continually doing other things that distract me). It's not that I don't want to clean up after myself, or finish eating, but it makes me feel bad that I forgot something so obvious. Like I walked past it 10 times in the past hour and didn't see it there at all.

Other times its something that I was planning on doing and just haven't worked myself into it yet. For me this also feels like I lost track of time. "I'll do it in 5 mins...". I wanted to do it but I didn't get around to it before it was pointed out to me. Not being able to manage my time and realize that that 5 minutes was actually 2 hours is the problem with this one.

One thing that might help is the way you remind him. Telling him that it's so easy to just rinse his plate and put it in the dishwasher. "It only takes 15 seconds" can come off as condescending. Gently reminding him might work. It works for me. "Hey. Can you wash your plate when you have a few minutes/before bed."

Not sure if this helps but here it is.