I feel your pain - my son has high-functioning autism and his 2-year old meltdowns are burned into my brain with fearful clarity. Hmm, offend relatives or provoke one? No contest.
One of the problems with meltdowns in autistic toddlers is that they look so much like normal toddler behaviour, just spectacularly bad. I vividly remember the looks of disgust I used to get in the street or the supermarket when my son threw himself on the ground and screamed. It simply looked like he was having the mother of all tantrums, and the looks plainly said "Why doesn't that mother do something about disciplining that child?" He was undiagnosed at that point, just to make it worse. It was a big relief when he grew big enough that it was obvious he had some sort of disability when he melted in public.
If it helps...
At age 3, my son was totally non-verbal, not toilet trained, unable to do basic self-care like wash and dress himself, and having horrendous meltdowns lasting an average of 1.5 hours (his all-time record was 2.5 hours). When things were good, he would have 3-4 of these a week. When things were bad, he would have 3-4 a day. Cleaning his teeth was a half-hour ordeal; washing and brushing his hair was so hideous I got his head shaved.
Today he is 12. His speech is "off" in his choice of words and inflection, but perfectly understandable. He understands, and even makes, jokes involving puns and sarcasm. I am regularly complimented on his excellent manners. He only needs verbal reminders to wash and change his clothes. He has been attending a normal school, with the assistance of an aide; he is looking forward to starting high school in February. He performs chores around the house, rides a bike and can safely walk or cycle to school by himself. He walks to the shop to spend his pocket money, chooses his sweets, pays for them and walks home - all totally independently. He plays with his friends and has sleepovers at their houses. He has a crush on a girl. He loves Harry Potter and Monty Python and is currently reading Eragon. He is excellent at roller skating. He dreams of becoming either a paleontologist or a wildlife park ranger.
Congratulations on recognising your son's unique needs and being willing to cheese people off to meet them. Autism is a hard row to how but your positive attitude, coupled with such an early diagnosis, will give your little boy the best chance he has to live an independent and successful life. Well done, and good luck.