Mothers Day is for Mothers-in-Law too.

A mother is a saintly sort
who cares with no reward,
she soothes her children's fevered brow
and comforts with a word.
Her fragrant presence
is a blessed boon
to all who come her way,
So you must not say those bad words
when your wife's mom comes to stay.

She doesn't mean to cause discord
when she tells you you're a bum,
or tells you you're giving her a headache
when you try to sing or hum.
She means to do her best for you
when she gives her sage advice,
So on Mothers day when she comes to stay
don't cuss at her, be nice.