S.H.
My 18 month old just started this too. his sister was being silly and showed him to do this. Also, we are trying to give up the pacifier and this might have something to do with it. He is also trying to bite alot as if he is daring me to go get the pacifier. I think that he thinks that if he is gross enough I will give in. Please let me know if you get any advice because I am right there with you and tired of changing his shirts all the time.