This isnt a new one to me folks, whilst ive been diagnosed diabetic for 8 months ive had a garlic allergy for nearly 10 years and trust me when I say there is garlic in more things than there is sugar.. The key here is to wear your diabetes stripes with pride and tell the world you have it prior to ordering anything.
With Garlic I would make the waitress aware upon first being seen that I have an allergy and unless they want me to blow up like a puffer fish and have an ambulance here i'll need a little more looking after than the regular Joe; I then ask the waitress to go back to the kitchen with the menu and let me know what is safe to eat from it and still question some of the responses.
My point here is don't feel awkward or victimised by your disease, feel liberated, you're now entitled to special treatment! Announce it and demand to be treated like a king! You are the customer and the food and drink you consume in a restaurant should be nothing less then first class.
I always feel that customer service is 80% of the experience of a good meal. Show your stripes when you enter the establishment, that way should you receive anything in error that could seriously affect your well being the onus is very much on the establishment to explain, why when you made it so clear that it was a health risk to you would they think it was acceptable, and how are what do they think they should do to rectify their error...
Many of my meals out have been free, many places I return to because they look after me and as soon as the waitress comes over shes says no garlic right? what can I get you.
Cheers Andy