Here's the rule that I think is THE most abused rule in the game of disc golf: I call it the "Foot Fault". Here's the PDGA rulebook description of the rule-
A. When the disc is released, a player must:
(1) Have at least one supporting point that is in contact with the playing surface on the line of play and within 30 centimeters directly behind the marker disc (except as specified in 803.04 E); and,
(2) have no supporting point contact with the marker disc or any object closer to the hole than the rear edge of the marker disc; and,
(3) have all of his or her supporting points in-bounds.

B. Stepping past the marker disc is permitted after the disc is released, except when putting within 10 meters.

C. Any throw from within 10 meters or less, as measured from the rear of the marker disc to the base of the hole, is considered a putt. A follow-through after a putt that causes the thrower to make any supporting point contact closer to the hole than the rear edge of the marker disc constitutes a falling putt and is considered a stance violation . The player must demonstrate full control of balance before advancing toward the hole.

And its not limited to just newer players. I've played in tourneys where the top guys on the card were the worst offenders!

Agreed!

Joe does this all the time!