DS1 has AS, Dyspraxia and the same weird hearing thing that I do which means we can't 'tune out' extraneous noise, we lack the 'cocktail party hearing' function so when we have conversations they tend to be on the loud side. I am also partially deaf so have trouble regulating my own volume and as such, both the DC have grown up used to things being loud. Added to that my insistence on using the same vocabulary with the DC that I do with my peers and I'm sure I probably come across as a pretentious twat at times.
Not in the supermarket, because they are hell so I get the nice man in the van to deliver it for me, but on the bus or in town yep, we absolutely prattle on most of the time. Because of the way DS1's brain is wired and his short attention span though, our conversations end up being so bizarre that I'm sure more people are wondering WTF we are on about than are thinking I am showing off.
A typical 25 minute bus ride conversation would cover topics like the coal miners strike, Proportional Representation, giant squid, Pokemon cards, PC vs Mac, gender inequality and that funny thing that happened in the Simpsons last night (actual example from last week). Each topic shift makes total sense to DS1 and me at the time, as he has quite a convoluted way of thinking and one aspect of a subject sends him off in unexpected directions and we are both so used to this it seems perfectly normal. It is usually only when DS2 (NT) asks how the conversation started that we tend to realise how disparate the topics were. Still, I have never had any comments on it from other bus users, apart from the occasional little old lady saying how nice it is to see a mother engaging and educating her child, and I like to think that if anyone has been unfortunate enough to be trapped within earshot , that they might have learnt something themselves 
On the plus side, my DC have an excellent vocabulary for their ages which helps them be understood by other adults and to engage at an adult level. The downside of that is that I am so used to explaining what words mean after using them in context ie "we've covered quite a disparate, that means very different from each other, range of topics haven't we?" that I do it all the time. To everyone. I have been walking through town sans kids with DP before now and been doing it and he has to stop and remind me who I am talking to 
I think there is often a clear difference between educating your child and being a pretentious twat though. Using the post office example from up thread, I might have said "this parcel is for Granny, but the people in the sorting office don't know who Granny is because lots of people call their grandmother Granny, so we use her proper name. Yes Mrs X at school is called Mrs and Granny is called Lady. There are lots of titles people have like Mrs, Miss, Lady, Sir, Mr, Reverend and Doctor. Yes Uncle Pete is called a Doctor but he isn't a doctor like the man who gave you medicine because he is a doctor of Biology. You can get a qualification called a doctorate in lots of subjects which means you can be called a doctor so not all doctors are medical people. Yes that is a bit confusing, I suppose that is why some people in America are quite specific about doctor and medical doctor."
Long winded? Hell yes. Pretentious? Depends on your ideas about further education and Uncle Pete's PhD really Loud? Quite possibly. Way better than a 10 year old with a loud voice repeatedly asking the same question and going into meltdown if he doesn't understand the answer? Your call