I've heard the standard "Nice M3" a few times. Once by a porter at the BMW dealership, which I thought was kinda odd, but I guess they're not selling or servicing the cars so don't need to be able to tell them apart.
Haven't really got into any conversations with anyone telling me the car is slow, or "just" a 1 Series, etc. Seems materialistic and "one-uppy" and, frankly, pretty juvenile. Maybe I just don't associate with those kinds of people at 35 years old.
Actually, I sort of get the impression from many people that they think the car cost more than it actually did. Most people I know are pretty frugal when it comes to cars and, if anything, think my car is too flashy.