So many great and hilarious comments here, but the sociologist in me just has to make a serious one about "why do they do that?" They do it because patriarchy is a dominance based hierarchy where if you don't "win" in every interpersonal engagement you "lose." Insecure types who are still deeply bought into that social system feel like they have to flex around everyone (that they aren't already sure they are inferior to) just to keep reinforcing some imaginary pecking order to themselves. Apparently, there are extra points in their mind for making a well-known person look stupid (even if they are actually the ones who look that way).