Continuity mistake: Dick's plot in this episode is that he learns about the concept of tipping. However, the season 3 episode "Eleven Angry Men and One Dick" showed that Dick was already familiar with the concept of tipping when he tipped a bailiff during a jury selection process.
Other mistake: While talking to his therapist, Dick tells her that one of the mishaps that he caused in his relationship with Mary was showing up to a fundraiser naked. While true, this doesn't happen until Episode 13 (Rutherford Beauty) - two episodes later. This was due to the fact that most of Season 5 was aired out of production order.