I used this one a while ago...
Two nuns were sitting on a park bench, enjoying the scenery of family's playing and ducks quaking.
In the distance they see a man approaching, wearing what appears to be only a trench coat. They dare not say what they were thinking he may be doing.
Soon the man approaches the two holy nuns and opens his coat. As expected, he is stark naked and flashes his privates to the two sisters. Both were instantly in shock of the situation, so much so that one of the nuns suddenly had a stroke.
The other nun though couldn't reach....
Buh dum tish!