Pigs are very sweet to me because it is one of my family nicknames! I know it may seem like a cruel one, but I assure you, it's not!
I guess I kicked a lot when my mother was pregnant with me, so everyone nicknamed me 'piggly wiggly.' When I was born, it got shortened to 'Piggy,' especially after the arrival of my little brother, who became the 'wiggly.'
Over the years, it just became 'pig' or 'peg.' :-)