Not all violations are equal, and it isn't necessarily the violations that yield the biggest advantage that are the ones that get to me the most. Rather, it's the ones that are small but frequent, or ones that aren't done all the time but only when it makes a difference. And there's other stuff, too.
1. "One". At goaltimate recently, I called "fast count" when the marker started by saying "one", then allowed the count to get to five in order to call a foul. (This happened after about 8 minutes of playing, after telling myself beforehand I wasn't going to be a Billy B rules jackass.)
2. Jumping offsides on a pull in order to throw it farther or to get down faster to set up a cup or disrupt the first pass. Perhaps oddly, I don't mind if you're offsides if you're just doing it to be lazy.
3. The sidelines yelling "Nice D" after a brutal mugging by the marker on a break-mark attempt. In a parallel world, I might compliment that team on its honesty in admitting that they're cheating, but in this one, it almost always makes me mad.
4. The "handler hop." I'll call a travel on this every two or three years. A handler will catch a swing pass standing still, then will do a little hop to the continuation side.
5. The no-pivot-foot pivot. You all know this guy. He steps out to fake a backhand, then follows with his pivot foot as he turns back to the forehand side. This enables him to throw a forehand more quickly. I can think of one guy who does both 4 and 5 and averages well over one travel per pass (I only name names when I am personally aggrieved, btw).
6. The auto-fake. Ok, this isn't a violation, other than being an offense against good ultimate. Catch a swing pass, then automatically fake the continuation with a big backhand windup. If you do that three times in a row, it ought to be a turnover.
7. Pulling out of a line of cars, driving the length of the line, then cutting back in to wait in line closer to the front.
8. Pulling into an intersection knowing that traffic is blocked just in front of the intersection, resulting in gridlock. I swear, if I have a terminal illness and no assets to pass on, I will make it my life's work to ram people who do either of these things.