A friend told me he once had two JW ladies visit his house while he was in the front yard. One was an older lady, the other young and attractive. My friend (who looks pretty rough) walked up to them and gestured to the older lady "You - ***k off! then to the younger one "You- get inside!" Needless to say they both left rather quickly...
I think this is a good precedent. So: "Fred - ***k off!" (But leave your sister here [ that is, if you've finished with her yourself!])