obligatory #css crimes suggestion! it's a fun little tag to browse from time to time filled with various gizmos that work straight in cohost. also worth mentioning #interactive
As an inaugural tag of the day, #css crimes is extremely appropriate. It's absolutely one of Cohost's signature features 
, to the point of getting long form news coverage:
::slaps top of website:: this bad boy can fit so many css criminals
I am not personally a CSS Crimes, like, afficianado, but here are a couple that I have seen making the rounds recently:
(Feel free to comment with or rebug with your favorite CSS crimes!)