Nerds then: A highly studious individual who lacks social skills or an incredibly intelligent and skilled expert in certain field(s) with a generally shy, awkward, or introverted personality.
(Edit: although being shy/introverted may not always be a necessity)
Nerds now: People who feel the need to take the most mundane media, technology, or pop culture-related things and plaster "I'm such a nerd!11" after every single observation regarding fandom, technology, or video games.
"That guy's blue hat looks like Sonic the Hedgehog! Oh my god, I'm such a nerd! XD"
"I recognize that logo from Zelda!!! I'm such a nerd!"
"Just bought myself Modern Warfare or another extremely popular game. Gosh, I'm SUCH nerd! XD"
"lol picture of myself in thick-rimmed glasses in a cute pose I'M SUCH A NERD, GUYS."
"i keep takin pictures of myself in glasses and oh my god im so nerdy and the most awkward person i know let me just take six hundred more photos to show all these strangers what an awkward goofball i really am god im so nerdy and outlandish also did i mention glasses"
"Oh shit, just got s special brand of electric toothbrush for my birthday and I LIKE IT! Hear that society, I like getting this special brand of toothbrush or other technology-related item and automatically declare myself a nerd despite knowing absolutely NOTHING of its detailed mechanizations or functionings! LOLZ SUCH A NERD I AM!111"
Congratulations for recognizing your exclusive uniqueness as a "nerd" by recognizing and drawing similarities to a widely popular iconic video game character that's been around for years that everyone and their mother knows the name of.
Buying and playing an incredibly well-known game title owned and bought by millions of people all over, oh my, how incredibly nerdy of you. Let me just get my nerd repellent because I just can't handle the level of social awkwardity and nerdishness that must surely be emanating from every fiber of your being.
Face it, "nerds" have gone from being awkward people who actually had the intellectual capacity to make genuine technological or progressive contributions to society to "lolololz iiek vidjagames and i recognize the tardis on that t-shirt SUCH A NERD!!1111 XD" (even if your grades happen to be, in fact, extremely mediocre or just plain shitty).
Oh, and glasses. Can't forget the glasses.