Can you tell who's Grandson he is??

My father (okay, and my sister, too) is notoriously known for drinking out of the milk carton/juice container at his house. In fact, I'm not so sure that I haven't caught him doing it when he's come to visit us a few times, as well... It's something that drives my husband crazy, and a portion of my Beutler upbringing that I did not carry with me into marriage. :-) I was quite amused, therefore, when I walked into the kitchen one day to find that Grant had found the near empty 2-Liter of Pepsi from our pizza night the evening before and was gingerly finishing it off...It must be hereditary, afterall! He's definitely never seen his mother do it! Ha!