Such testosterone-pumped viewers click on the thumbnails, only to be disappointed by a completely random (and often ad-infested) video.
Not surprisingly, such videos often make it to the "Tio Viewed" list, thus exponentially increasing its number of victims.
To the horror of many, this can also be combined with being rick rolled.
Of course, females can be the victims of the thumbnail cheat as well (although more often out of curiosity than horniness.)
Note: I'm not trying to be sexist about guys in general. Still, how do you account for those millions of views on such videos or the pissed off comments left by male users? ;o
*Rick Astley's funkalicious "Never Gonna Give You Up" comes onto the screen*
Male User: NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
not this ginger again/ the thumbnail cheat!! *bangs head on desk*