Crane Flat to Half Dome?!? That's probably a little more than a day hike...
My pet peeves:
1. Incredibly large groups hiking together (usually some school group or foreign tour group). These people usually show no respect for their surroundings or other hikers and generally act like they are at the mall. Yes, you can avoid them by going on longer or more strenuous hikes, but it is a shame than some parts of Yosemite are continually affected by this.
2. ANY trash alongside the trail.
3. People who insist on camping in prohibited areas. Especially the Lower Cathedral Lake campers who insist on setting up camp 10 ft from the water. (Also usually using a bear bag...) That's at least 3 rules broken at once, and it ruins a lot of pictures...
4. People who drive 15 miles under the speed limit on Yosemite roads and refuse to use the turnouts. (I don't speed...)
5. People who think it's okay to drift 3 ft over the yellow line while driving their gigantic rented RV around the turns. If you are going to drive an RV or pull a trailer, mountain roads are NOT the place to learn how...
6. The guy who goes up to Glacier Point and hauls $10 million worth of camera gear with him, stakes out the corner spot on the right side of the lower lookout deck at sunset, then tries to start fights with everyone who tries to stand in "his" spot. Hey buddy, my mom has never seen Yosemite and deserves this view as much as you. If you were a real photographer you would go find a place by the little Geology exhibit AWAY from the hordes of people.
7. People who go to Yosemite to party, drink, stay up late, and generally pay no attention to their surroundings. There are plenty of other less visited/less beautiful places for this type of activity. Do not spoil it for those who have traveled around the country/world.
Enough soapbox, though... Despite all of that I still love Yosemite and will keep coming back.