Allusion sought.

I'm trying to think of a play or movie where there is a character who has two identities and then comically (or dramatically) gets mixed up and says or does something in the style of Identity A while presenting himself (or herself) as Identity B. An example would be if Superman forgot he had his outfit on and acted nerdy and ineffectual like Clark Kent. It seems like something that ought to happen as a plot device all the time, but I can't think of a single example. Try to come up with something specific, not just something like one time Don Diego acted like Zorro...