Not a big deal to me. Smudge is so big I can understand why people think he might be a "mini collie". Before we got Gizmo we were actually looking for a collie and ended up with a sheltie. So...nah. They're usually just trying to make conversation, and they like my dog. I don't understand why that would make me mad?
However, when people ask if Fluffy is a border collie... I could understand MAYBE if she was a bi black, but Fluffy doesn't have much white on her at all. Her collar is only 3/4 of the way around her neck, and she has almost no white on her feet. More people get Fluffy's breed right than they get Smudge's right. 9 times out of 10 people will ask me if Smudge is a collie. I've only had one wrong guess on Fluffy.
I'm guilty as charged.

I've stood at one end of the house, whistled, and yelled: LASSSSSSSSSIEEEEEEE!
I got a kick out of it when they both came running.