thumbnailer 

term used to describe a person that appears to be attractive in a thumbnail picture on a social networking website, however, the full size image reveals their ugliness.

sometimes used to describe if you would have sex with the person if they did, in fact, look how they do in the thumbnail image.

goes along with the trend of people always placing the image they look best in as their profile picture.

I was browsing Facebook today and ran across what i thought was a cute girl. She looked good in the small picture, but once I clicked on it I found out she was a thumbnailer.

thumbnailer by Linger May 20, 2009

Thumbnailer 

Someone who only looks attractive in a thumbnail picture...until you click to enlarge.

Guy 1: Damn dude this chick on Cindy's page looks nice.
Guy 2: Click her and lets see!!
Guy 1: Okay bro *clicks*
Guy 1 and 2: Oh my damn, its a thumbnailer. Tricked!

Thumbnailer by CarlRosta July 8, 2011

thumbnailed 

When someone looks good in a thumbnail picture, and you click on it only to find out they don't look nearly as good in the full picture, you've just been thumbnailed.

"Ooh, she looks hot."
*click*
"Dammit! Thumbnailed again!"

thumbnailed by ibbit June 28, 2009

Thumbnail 

The cover photo for a YouTube video. Usually to get your attention or show what the video is about.

Put boobs in the thumbnail to get more views dude!

Thumbnail by TheRedBeanie__ July 20, 2016

Thumbnail Syndrome 

The phenomenon in which someone seems far more attractive in the thumbnail version of a profile picture than they truly are.

I thought the girl who sent me a friend request was hot, but it turned out to be a case of Thumbnail Syndrome.

Thumbnail Syndrome by Ken_II July 27, 2009

Thumbnail Hot

When someone looks like they might be attractive in their Facebook or Twitter thumbnail until you click on it and find out that they're really not.

"Yeah, at first I thought he was really hot but turns out he was only thumbnail hot."

Thumbnail Hot by jeatags March 31, 2009

Rule of thumbnail 

A rule of thumbnail is a principle that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or determining if a Facebook profile is worth clicking on based on it's thumbnail.

Guy 1: Have you seen that chick's face?
Guy 2: No, i thought she wasn't worth looking at, according to my rule of thumbnail.

Rule of thumbnail by starterel March 21, 2013