Try using when the two big bods come in

I don't see how you could really get in trouble for that - i'd think that the worst possible outcome would be that you may be asked to apologise for using the phrase - but given that it was not delivered to their faces - and if you think like that it is probably evident and they are aware that you think they are idiots - I am struggling to see how much could really be made of it?

I think it would fall into insubordination , disregard etc