Following up on the mistaken for a prostitute thread:
Twice when I was younger I was mistaken for the valet at some upscale restaurants. Once I was outside grabbing a smoke, another time just waiting to be picked up. I don’t know why either, I wasn’t well dressed, but I wasn’t wearing an orange blazer or anything like that.
Far more often I’ve been mistaken for a construction worker or an axe murderer, but I really did look the part in those cases.
In a fast-food restaurant once in a high-viz yellow motorcycle jacket and black rain pants/boots, some old lady thought I was a firefighter.
My unpaid internship adviser mistakes me for someone who likes Mathematics. Or I am mistaking my unpaid internship adviser for someone mistaking me for someone who likes Mathematics?
Due to a poor combination of clothing choice and location, I was once mistaken for a Target employee (in Target).
Exactly. Don’t wear khakis and a red shirt to Target.
I was once mistaken for a cop, more precisely a detective. Mind you, I was in a black trenchcoat and fedora. 
I went to vote on my way to work, but as soon as I entered the polling place an election judge told me to go across the street. 
I was almost to the door when I saw the “Vote Here” poster and turned back. The election judge explained that she thought I was going to the police conference across the street but picked the wrong door.
I don’t wear my bright green Eddie Bauer fleece to Jewel because their employee jackets are also bright green fleece. 
I was once mistaken for a murderer (and my client mistaken for a lawyer) during a trial where he looked older, wiser, and better dressed than I did.
WOW!
I have mistaken my unpaid internship adviser for a robber. Is it a mistake?
When I was working for a beverage distributor, I was often mistaken for a grocery store employee.
Them: blue jeans, white polo and neck to knee green apron. (Or whatever was the case for the store I was in)
Me: grey slacks, white, red pinstripe uniform shirt and Snapple cap.
Totally alike.
I third this. 
The good news is that he went off to prison, and I went home.
You think that’s bad, I was once mistaken for a K-Mart employee (in K-Mart).
Some guy with a thick Indian? Middle eastern? some sort of thick accent walks up to me and says "You can help me?"Not wanting to be a jerk and thinking maybe he just wanted someone tall to help him get something off a high self I was all “Okay?” Then he says “you work here?” And I’m like “No.” And he’s like “Oh okay” and walks off.
I don’t think I was dressed in a way that looked like a K-Mart uniform, but honestly, I’m not sure what K-Mart uniforms even look like, despite shopping there sometimes.
Years ago, a group of women from work used to meet on Saturday a month at a local breakfast buffet and hang out, shoot the breeze, laugh, eat, and generally raise a bit of a ruckus. One morning, an older man came over and said something about us realtors not letting the guys have breakfast with us.
OK.
We were all engineers, technicians, and other folks who worked at the Navy aircraft rework depot. Needless to say, we all gave him rather perplexed looks. And that’s the tale of how I was mistaken for a realtor.
And years before that, when I was all of 17 and working in my dad’s office, he sent me to get some papers signed because they were urgent. I had to fly from Baltimore to Minneapolis and back in one day. When I got there, the secretary of the man who had to sign the papers took me out to lunch. She asked if I wanted to order a drink, and she was surprised when I told her how old I was. She was certain I was in my 20s. That’s the first time I was mistaken for an adult!
When I was younger, I was once mistaken for a member of the Oak Ridge Boys who I bore a resemblance to. It was the one with the low voice, so I obliged with a snippet of Elvira (and autographs).
When I was in Iraq, a miscommunication with a local barber resulted in my getting a ‘high and tight’ haircut’. As a result, I was frequently being mistaken for security personnel until it grew back.
I’m sometimes mistaken for a Spanish speaker.
And it seems like I’m always being mistaken for someone who gives money to panhandlers.
Good news for you, maybe. Client, not so much. 
I’m frequently mistaken for someone who gives a damn.
Otherwise, mistaken once for a Best Buy employee, under similar circumstances to Asimovian.
I’ve been mistaken for a doctor before.
I have been mistaken for Dr. Demento at a convention where he was attending. I have one of those faces: I’ve been mistaken for a TV weatherman, an elementary schoolteacher, a real estate agent, a comic book store owner and an escaped prisoner. Around Christmas kids insist I’m the real Santa Claus.
The one time I attended The Grand Old Opry, I went to get Madame P. & myself refreshments between the 1st and 2nd show. One of the concession stand workers asked me if I wasn’t in the next set.
I am usually mistaken for a supermarket employee, which I was for 40 years until I retired. I guess I just have THAT sorta’ face. When I’m doing MY grocery shopping I get asked all kinds of questions and field requests for help.
My brother, when he was younger, used to be mistaken for Mike Schmidt, the baseball player. Sometimes people wouldn’t leave him alone unless he’d pose for a photo, or give an autograph. So just to make them happy he’d oblige.