Idle boasting

Be proud your forebears were hanged for stealing sheep,
they're nuisances, and their bleating is so loud;
they worked to make sure that we all could sleep,
and did not seek the plaudits of the crowd.
We'll be so happy, quite over the moon, my dear
if you would take a look at our family story;
consider now the most distinguished forebear
who was touched, if only for a moment, by great glory.
So, you've a great harridan as your dear mater,
but don't be discouraged by that grisly fact;
your forebear once spent some time with a traitor,
do mention that, but please, only with tact.
Pride in ancestry is fine, but does not work
if all you're doing here is being a jerk.