A Flock Of Sheep!

My new word for a flock of sheep is:

A 'Painintheass' of Sheep.

Because that's what they are as you're happily driving down some picturesque rural road, and the road is only wide enough for one vehicle, and you're happily plodding along at a quite slow pace, then, as you round a corner you're confronted by three hundred sheep being herded from one field to another.

A Painintheass of sheep.