Khloe, Kylie, Kendall and their friends were certainly having a lot of fun during the family vacation to the Dominican Republic on "Keeping Up With the Kardashians" (Sun., 9 p.m. ET on E!). But in one instance, it was at the expense of their mother, Kris Jenner.It was a long prank, as the girls dragged Kris out of bed, and on a carpet through the house until they threw her in a shallow pool of water.