When I was younger, thinner and in Vegas I was stopped by some guys wanting to know “Which issue?”
It took a few minutes to remember I was wearing a Playboy shirt.
Mildly flattering, but it’s not like that happens now 
He won’t outright claim it but will milk it when he can. There’s a local Starbucks where the barristas shriek “Marky Mark!!111” when he goes in. (I stay in the car. His ego doesn’t need more stroking IMO. )
About 10 years ago I was shopping in a high-end clothing store looking for 1 elusive item, but it was just crazy expensive. I was very casually dressed-almost no makeup, but I kept getting crazy help from the employees and even got a glass of wine.
As I was checking out with my 1 painfully expensive item, one of the clerks asked if I would sign an autograph! Apparently they thought I was Jodie Foster, which killed me as she’s older than I am, and I don’t think I look anything like her.
I paid with my credit card with my name on it, told them they were mistaken, and damned near ran out. Now I would have laughed and thanked them for the flattery.
Britney Spears. I have to keep reminding folks that I’m the mature one.
Once when my hair was red I was mistaken by a salesperson for Dottie West, but I think she was just trying to sell me a pair of boots.
Jack Osbourne, when he was tubby.
It doesn’t happen so much anymore, but during my college years various people told me I looked like (a) Jack Nicholson, (b) Steve Martin, or (c) John Cleese. But not really enough that I would ever be mistaken for them.
And one time at work years ago, I got a call from someone who somehow thought I was Ray Charles’ manager. 
Does voice count? I’ve been told several times in widely-separated contexts that I sound like Kermit the Frog. This is not a compliment.
I wish I sounded like Spoons.
Qadgop, I don’t know you.
But from your postings here, I respect the hell out of your expertise and contributions to society, and in no way wish to disrespect your past troubles with alcohol (which you have honestly and bravely shared with us).
And, for some reason, the thought that there may be guys out there convinced that they once got hammered with Donny Osmond brings me untold joy.
I get mistaken for John McEnroe all the time. Only recently found out he is over 6 feet tall, while I am about 5’8. I guess no one else knows that either
One time a drunk guy was going on and on and I had enough, so finally I offered to sign an autograph for him before I left.
Which I did.
And he immediately said “I always thought you were left handed”
D’oh.
I told him I play tennis left handed, but do everything else right handed. He went home happy. And I went home with my gf who pretebded to be Tatum O’ Neal that night (it was a long time ago!)
About ten years ago, I was at the McDonald’s in Breezewod, PA with some friends.
A group of locals girls were giggling. The lone female in our group told me that they were giggling at me, but didn’t know why.
We went over and talked to them. They were convinced that I was the guy with the deep voice in the Oak Ridge Boys. I had been told this before, so I knew his name (Richard Sterban).
I denied it at first, but realized that the greater good was for them to think they’d met the real deal. (The fact that I was carrying a guitar pretty much implicated me). I have a pretty deep baritone voice, and can pretty authentically sing the bass part in “Elvira”.
I signed autographs/forgeries on napkins.
I used to look like Pat Cash. I also used to wear a checkered headband!
Giddyup!
Ooom-bup-a-ooom-bup-a-mile-mile!
Yes, Gary Cattell (I still remember his name). The funny thing was that when I started at Penn State I was 16 and he must have been a lot older than that, but the resemblance was very striking. Later on I kept getting taller and I noticed I was only mistaken for him when I was sitting down.