Jericho wrotedeefstes's joke is that two violinists can't play in time (the second one is off key and 3 beats behind).
Just to clarify, in an orchestra the violins are typically divided into two sections; the first violins and the second violins. The more intricate violin work is often expected from the first violins while the second violins usually play the more "mundane" harmonic parts and accompaniment. The more accomplished or senior violin players in an orchestra will usually be playing first violin.
It is a common joke in orchestras that the second violins are dumb or less musically gifted (if at all). In choirs this label is often applied to the bassos or altos and in guitar circles this label is often applied to
Jack Flash Junior bass guitar players.
As an aside, I'm not sure if English has a similar expression but this is where the Afrikaans expression comes from "om tweede viool te speel" (not being offered the opportunity to take the limelight).
