Maybe this has happened to you. Out of the corner of your eye, you spot what you think might be, could be - even though you know it really can't be - the Unabomber.
At a grocery store.
Or a mall.
As it turns out, nope, it's just some kid in a dingy sweat shirt, with the hood up.
But who can tell?
It's crazy out there with hoodies. Just who isn't wearing one these days? Suburban moms sport them. So do skateboarders. Even NFL head coach Bill Belichick wears a hoodie when he prowls the sidelines.
One hoodie might feature Scooby-Doo on the front. Another, a communist red star. Still another, a probing quote by Confucius.
HOODIE CRAZE - You have got to love the mass appeal of the hooded sweatshirt, especially if you're a manufacturer. CNS Illustration by Cristina Martinez Byvik.
Got to love the mass appeal of the hooded sweat shirt - especially if you're a manufacturer, or if you're selling the expensive designer versions.
But what's the secret with them?
Why wear one with the hood up, particularly in sun-splashed, balmy Southern California?
Why wear it with the hood up while indoors?
Is there some kind of solace in there?
And what's with some hoodie wearers trying to look bad and menacing - even if they're 40 and have a mortgage?
These days, people walk through stores and schools, hoods up. They sit in restaurants and coffee shops, hoods up. They're hiding out, in plain sight.
Or maybe not.
"It's comfortable, like I'm wearing pajamas," said Tyler Hanson, 16, who was wearing his hood up when temperatures were in the upper 60s.
One teenage girl said, "I just like the hood up," before glaring from under her hoodie and walking away.
Grace Crowell, 15, said some kids wear them up to hide iPods from teachers. Her brother, John, 16, said he wears his hood up because his ears get cold easily. His knees must be more weather-hardy because he was wearing shorts when we talked.
And, sure, some people wear their hoods up because they're aiming for that thug look - or because they are thugs.
Some school districts on the East Coast and some shopping malls in Britain ban hoodies because authorities can't see who's under them. Security cameras basically become useless.
Young people might be attracted to hooded sweat shirts for reasons beyond fashion and popularity. Something deeper - which they're not even aware of - could be pulling them.
For instance, many kids aren't happy with their looks, said Dana Nurge, who teaches criminal justice at San Diego State University and is a technical adviser to the San Diego gang commission.
They go through geeky stages. At times, they want to disappear.
Hence the hoodie.
So while children might appear more menacing in their hoods, that's often not their goal. They're actually hiding insecurities, she said.
"A lot of kids don't like to be looked at."
Nurge has students who sit through her class, hoods up. Some of them are her best students.
She's asked them why, and they tell her it's simple. They like them.
For inner-city youths, the hooded sweat shirt can be a survival tool, Nurge said. Giving a wrong look to the wrong person can bring trouble, so they put the hood up to avoid making eye contact with anyone.
"There's a broad range of reasons why they wear them," Nurge said.
How about to actually stay warm?
Maybe in Wisconsin.