Gender-bending incidents are classified into one of four categories based on how significant they are to the reader/viewer experience. The significance of each story is equal to that of the most significant incident.
Not only does the gender-bending happen a lot, it's central to the plot. (eg. Stories like Ranma ½ where it's part of the driving conflict)
The gender-bending recurs/continues for a significant portion of the story but is not directly integral to the plot. (eg. A character who, for comedic relief, finds it difficult to remain one gender)
The gender-bending is significant to the plot but is restricted to a small portion of the work (eg. a single story arc in a long-running series) or gets extremely little focus.
The character or incident in question appears only briefly (eg. a one-shot gag) or very little focus is given and has little or no significance to the greater plot.