Armpit wipe

So a very funny/wierd thing that Ryan does is the armpit wipe. It all started about a year ago when we were at the Little America Restuarant and Ryan was going to eat his meal and I saw him pick up his fork, wipe it is his armpit and then start eating. I asked him what he was doing and he informed me that he was "cleaning" his fork to eat with it. Of course being the MATURE parents that Dennis and I are, we started laughing out heads off,(I mean who thinks of thier armpit when they want something clean) and said something stupid like, you could wipe it in your bum also if you would like! of course he got mad at us and to our great luck, the waitress came at that moment and saw that Ryan was upset and asked him why. Being the honest kid that he is, he informed the waitress that we just told him to wipe his fork off in his bum!! I know, our own fault. Anyhow, for some reason this method of cleaning his utensils is a instinctive habit. We are constantly catching him picking up a utensil and wiping it in his armpit to eat with it. I am not sure how he pick up on this or why, but he does it all the time. It is quite humerous, you have to admit.