Don't Push - S6-E2
Continuity mistake: While trying to take a new Family Portrait, after Cameron, Mitchell, and Lily shake out their faces, say cheese and take another photo, Cameron goes to look at the laptop screen and there's a closeup of that newest photo, but when he tells Mitchell to look at the screen it's a different photo - note Lily's goofy eyes, etc.
Answer: He has seen himself dancing, and is mortified at how bad he looks.