That's what happened to Jeremy Renner, star of The Hurt Locker and the upcoming sequel in the Bourne film series, The Bourne Legacy. (He also played serial killer Jeffery Dahmer in a biopic, but let's not go there.) While on a flight from L.A. to London, he accidentally took a Viagra instead of a sleeping pill.
Hoping to avoid jet lag, he downed what he thought was an Ambien, but turned out to be a Viagra tablet "given to him by a friend". A friend with a warped sense of humor? Apparently some Ambien pills share a similar blue hue with Viagra, but who wouldn't recognize the tablet's distinctive diamond shape? In any case, it was pretty surely not intentional on Renner's part, and it sounds like he was pretty miserable the whole time.
The flight crew were made aware of the situation, and did what you would normally do to keep any swelling down - offering ice packs. And probably blankets to help keep it under wraps.
Renner said he didn't get any sleep during the trip, which can take 10 to 12 hours, and had to endure an embarrassing walk of shame if he needed to use the loo.
A cautionary tale for any of you thinking of trying to use Viagra to set some kind of Mile-High Club record,