When you hear the annoyingly catchy tune of Carly Rae Jepsen's 'Call Me Maybe', and it's stuck in your head for the rest of the day/week/month/year/life.
A person who has been Jepsen-ed may experience irritability, nausea, and discomfort. Look out for sure signs of the afflicted humming the tune. If you don't run, you'll be the next victim.
Stu -- "Dude, what's up with Carl? He's been really grouchy and he's been complaining of nausea and pain.
Dude -- "Our buddy Carl was Jepsen-ed and he may never be the same."
* guy hears a girl singing 'Call Me Maybe' whilst walking down the street*
Guy -- "Stand back, foul creature! I will not be Jepsen-ed!!"