If you feel the need to start a conversation with "I don't mean to be rude but..." I really wouldn't bother. Because it will be rude. And annoying. And it will piss me off. Or I will just sit there thinking how rude you are and generally just be bemused in a what the hell type way as I was on Saturday. I got a panini for lunch in a coffee shop and a random older lady came up and "Excuse me I don't mean to be rude but would you like me to cut that for you?"
And don't just take stuff and do it for me, wait and be asked. Also more importantly when you do just take my shopping off of my lap and put it on the checkout don't then go off on one when someone assumes we are together and skips in front of you in the queue. Because 1) I would have preferred you not helped me anyway and 2) Taking over is rude and frankly I think it quite appropriate that you had people do annoying things to you as you did them to me.
Finally I'd like to point out that I am wearing a skirt today. And I am always aware of my clothes and catching on my wheels and things to be concerned about etc (unless its either new clothes or a new chair and I don't know about specifics). So 1) I don't need you leaning out of your car shouting accross the road to me that my "dress" is going to get caught in my wheels. Because obviously I checked I was right in thinking it was fine (and I was) but it is none of your business, very annoying and it makes me late because i get paranoid and stop every few minutes to check. and 2) i'm wearing a purple and orange skirt and a white t-shirt. It's a skirt. It's obvious it's a skirt. It's NOT A FUCKING DRESS!
If you're going to do the annoying unwanted advice to the crippled girl thing for the love of god at least get what you're saying right.