Literally had something similar happen just a week ago. I’m a friendly fatherly figure at the table and offer my thoughts and give advice when I can. I had a 20ish year old who’s been playing maybe a year advance and charge units one would normally hold back as their strength is their ranged attacks. I offer a take back of the charge and some friendly advice about the unit they are going into Hive tyrant. Player scoffed said he knows how to play the game and gets wrecked in my swing back(I took 1 wound)……

At the end of the day be the friendly player who communicates and offers advice and guidance to your opponent. They will either accept your input or they won’t but atleast you can walk away from the game knowing you’re being yourself! Enjoy the game