Having watched Sharknado when it premiered on syfy, I am pretty sure the director and producers did not ask the actors to act.
Sharknado is so bad, it is good!
Last film I watched was Niagara, with Marilyn Monroe.
She couldn't act either.
On the look out for anything with Terry Thomas, or Leslie Phillips that I haven't seen yet, in order to develop my 'good chap/total rotter' routine.