Why would a guy COMPLETELY ignore a girl (not even meet eye contact, rudely)?

there three possible answers to your question first one is he probably has no interest in you other than just another girl in his cl. possibly two he probably is interested in you but don't know how to go about asking you so he avoid a what could be embarring and awkward situation altogether. last but not least possibly three he like me or most men we doesn't show interest even to some that he might be interested in basically he like to be the pursued for better understanding of it's similar to Sasuke uchiha a character from the anime naruto. i have one suggestion for you if you wont to know interested int you instantly try sitting at his table in lunch or to be more direct you could ask him something simple like if he would like to go to McDonald's later that way you will get eye contact and he has to answer you right hope i helped a little.