I give it a B. Not because it was B material, but it was very inconsistent. When it was funny (and it was often funny) it was REALLY funny ("I'm afriad I am going to be surrounded by fatties!" " I'm not fat, I'm pregnate.").
When it wasn't funhy it was totally a C movie. Pretty dull and okay.
So it averages out to a B.
But, boy it was funny when it was funny.