Exactly why does Oliver not like Orlando in the beginning of "As You Like It"? I never seem to find a straight answer.
Oliver and Orlando are brothers, and it appears that Oliver is jealous of Orlando and simply dislikes him because Orlando is who he is. In the link below to Oliver's character analysis, eNotes mentions that coming up with a reason for Oliver's dislike of Orlando must remain "conjecture" as there really isn't a straight answer given for it in the text of the play.
Remember, too, that Oliver and Orlando are feuding brothers who serve to highlight another brotherly feud in the same play, between Duke Frederick and Duke Senior.
Check the links below for more information. Good luck!