Life is too short for ...

Bad books. (Or, probably books in general, unless they are textbooks.)
Not chasing your dreams, however scary, weird or hazy they may be.
- This one is important even if it sounds poetic or fictional.
- What if I took a break even if I didn’t know what dreams I’d go after during that period?
Work where you don’t regularly challenge yourself.
Learning random things. (Learn to build, not for the sake of learning.)
Being unhealthy.