In addition to keeping smaller aircraft from getting blasted by jets, another reason I park the small guys farther away is for spacing. It's not much of an issue this time of year at my airport (OQU), but when we're busy we need all the space on our ramp we can get. Our ramp is made up of concrete blocks that are 15' wide, and we have a list of how many "blocks" various jets and turboprops take up. If I'm expecting a lot of flights, I'll go out and count empty blocks beforehand so I can plan where everyone is going in advance. A Cessna 172 doesn't take up a lot of room, but if it parks itself in the middle of where I was going to park two jets, I might have to park those jets even farther away than I would have had to put the small guy. Also, it's easier to carry catering, coffee, ice, newspapers, and luggage to a jet that's right in front of the door.
I don't commit any of the other offenses on here that I'm aware of; as a pilot, I try to treat pilots (and passengers) the way I would like to be treated (parking and greeting them immediately to see if they need anything, pulling a warmed up rental right up to the aircraft door, etc.), and eventually when I'm on the other side of the line I'll treat line crews with respect as well.
As far as things that pilots do that drive me nuts, one is what Brian said; coming at me at an angle and then turning towards the flight line at the last second. This can affect spacing too if they end up a block left or right of where I intended. But the biggest thing that grinds my gears (and luckily doesn't happen too often) is when pilots completely ignore my marshalling signals. When Runway 34 is in use, the most logical way to get there is to pull forward and turn left towards the fuel farm/local parking, taxi to the end of the ramp, and turn left to taxiway A, followed by a right turn onto A. However, doing so can result in the local tiedowns getting blasted (along with anyone out there preflighting, or one of my coworkers refueling). Here's a picture in case none of that made sense:
The worst case was Beechjet that ignored my signals to turn right and went left instead, stopped after that second left turn, and gunned the engines to get going again, causing a 182 to wiggle like crazy in its tiedowns (I can only imagine if it wasn't tied down). Trust me, I know what the winds are doing, and I'm turning you right for a reason.