OP, those don't really seem like back handed compliments to me, they just sound like insults...
Sometimes I'll get the occasional riff on my car, but very rarely if ever have I had a complete stranger come up to me and say something mean about my car. Just seems like a completely rude thing to go up to someone you don't know and talk down about their car. The only strangers who come up to me compliment and tell me how much they love the color (Aqua Blue Metallic, by far the biggest amount of compliments I get are about the color).
As a 2LT automatic owner, of course I will sometimes get "shoulda got a v8". Or "why don't you trade it in for a manual" or "your car is awesome... except its an auto". But really thats it.
Honestly the only people who have ever said anything remotely negative are people who don't have as nice a car. One of my buddys friends who drives a 2012 Shelby GT500 would not stop going on about how great he thought my car looked especially with the color. It seems like those with nicer cars than me have more respect for my car than those than don't. Its usually people driving hondas and whatnot that give the snarky comments. Now most of the time people with crappier cars will compliment, but if there is a negative comment, it's from a guy in a 1995 civic or something like that.