If someone tries to "make" me like that, I just tell them I'm not who they think I am and they are making a mistake.It's not even running into "clients" off duty. In a lot of circumstances, you can see any thug and know he's a thug, just like a lot of them will know you're a cop.
The best is when you hear someone yell out "Hey Officer xxx. Don't you remember me?" And it turns out it's a victim or a victim's parent. But in the meantime, they've just broadcast to everyone that you're a cop, and you don't know who just heard that.
I also don't respond to anyone yelling out "OFFICER!" or whatever. I will casually look in that direction like anyone else but I won't acknowledge it was directed to me.
What's worse than that is your own family or friends doing that to you.
I met up with a few buddies for breakfast a month ago and we were hanging out before being seated and one of the guys walks up and yells out loudly, "How you doing, officer?" I just keep talking to the other guys without skipping a beat and not acknowledge it. He got it.