About T-Shirt Design
CATS - Because People Suck T-Shirt is funny without trying way too hard, which is probably why the idea works. It fits really well with cat lovers, but you do not have to be obsessed with that stuff to enjoy the joke.
It makes sense for holidays or casual days, especially if the person already likes this kind of humor. It has the same easy attitude people usually want from sarcasm shirts without sounding forced.
The sarcastic t shirt vibe is there without making the design feel too mean or over the top. It is an easy design to wear when you want something a little more fun than a plain shirt.