If you haven't seen the Leo Burnett "We are so excited about your pitch" video, then you are well advised to stay clear of it unless you wish to have your pride in adland lowered by a tier or two.
Now it's perfectly understandable that people want to make silly internal videos for comic reference and enjoyment. That is fine.
It's perfectly understandable that sometimes these videos leak out.
It's perfectly understandable that as an agency you are very excited about the prospect of a new client, and might want to show them your enthusiasm in an unusual way.
However. To make what is effectively an internal video of you cocking about and then have the idea to send it straight to the new or potentially even not yet won client... madness.
It's not about being serious, god knows some client love having a creative agency that is a little bit madcap and exciting; but is making a sub-Amarillo bit of amateur film the way to show your creative nous? Surely any creative director would see that film and tell it to get the hell away from the client before they delete every copy ever made.
All agency videos with staff dancing to pop songs. Just say no kids.