Question: Why did David get back in the shower with Mr Bean after hanging up the phone?
Answer: In the context of the movie, the "damage" has already been done, so-to-speak... he's already in the shower with Bean. And since he's also in a big rush to get to the museum, he decides to just keep showering. (In a meta, behind-the-scenes sense, it's also just funnier for him to stay in the shower rather than get out and wait for Bean.)
Answer: For acting suspiciously and acting as though he had a concealed weapon.
Ssiscool ★