Mcsillyster Share definition Flag A man who wants to be funny, but just can't at a certain moment in time. Ultimately leading to Non not laughing during class. "I want to make you laugh, but i'm a Mcsillyster :(" Mcsillyster by Winkwinkmcgee May 6, 2010 0 0 Get merch Get the Mcsillyster mug. Buy Now — $32.95 See more merch