There was a time when you could easily spot a douchebag by his wrap-around Oakley sunglasses and gelled spikey hairdo (see Ryan Seacrest circa the early 2000's for reference). But style evolves, making it harder to keep up with which guys you should aggressively avoid at your next singles mixer based on their appearance (of course, there are exceptions to every rule, but let's not take any risks).
There is, of course, an appearance by the man-bun. Warning: this video may or may not play like a time lapse of your terrible dating history. Sorry!
In summation, here's a brief recap of some of the douchebags you should avoid throughout history:
1940s: the guy with the creepy mustache.
1990's: the drunk frat guy with a puka shell necklace.
2010s: the man-bun who hits on women at yoga.