The poor viola tends to get the bits of harmony left over once composers have given everyone else the good bits. They also, and any viola players will kill me for this, tend to be the players who didn't make it to be violinists.
For those reasons, and others, this list of viola jokes is very funny to ex-musicians like myself.
However the following will hopefully have more universal appeal:
Why is a viola solo like premature ejaculation?
Because even when you know it's coming, there's nothing you can do about it.