It is impolite to drink directly from the faucet.
John has been working  for Jerry and John likes Jerry's daughter Cheryl.
John wants Cheryl to like him.
Cheryl invites John in for a glass of water, John tells her thank you  and rinses his g;lass when he is done.
Cheryl invites John in for a glass of water, John tells her he doesn't need a glass and John drinks from the faucet.
Cheryl appreciates John's politeness and makes a point of being there when he is.
Cheryl finds John odd and avoids John when he comes over to work.