I'm not really talking about anything super serious here (we've got another board for that) but I already see someone posting something like that anyway.
Anyway for me…
Vine related:
-99% of Vines feature rap or trap music, and if it's a Vine about a cartoon from the 90s or early 00s it'll feature a trap remix of the theme song
-Vines love to play up racial stereotypes in some way by people of said race, like black people loving Air Jordans and watermelon, or Arabic people making "surprise Jihad" jokes
-Anytime a "song based fad" comes up expect about 99% of Vine to get in on said fad with varying results
-There's a lot of "X be like, Y be like" Vines usually focusing on racial and cultural stereotypes, again with varying results in humor
YouTube:
-Downvote button doesn't work so things like racist comments might have 100+ upvotes from other racist idiots but yet the 500+ downvotes from non-racists don't show up at all
-Anytime you mention another Lets Player in the comments section of one Lets Player, expect to be berated for over 50 comments
-There will always be that one idiot trying to say "first!"
Know Your Meme:
-People will always associate Don the most with the site due to him being the mod people sorta just made the most visible