Lots of bad hikers and dog walkers as well. Hiking/walking groups that leave no room on the trail for other users. Dog walkers that can't control their dog off leash or even on leash.
As far as bikers, don't climb up Corkscrew on a busy Sunday with a group of 12. Don't ride loamy trails in the pouring rain or in the slush. Pick up a shovel instead. And turn off f*cking Strava.