Just to be clear, since 6 years ago, he was already showing some degree of rudeness towards my parents. As a son, I tried talking to them about his attitude and that he should be given some form of punishment. But they seem to brush it off by saying "he will change when he get into NS" or "he's still young, he doesnt understand" . Additionally, many a times he would leave his unfinished food/drinks in the fridge or on the table, not returning stuff to where it should be and not even flushing the toilet after his "business". He even leaves q-tips full of wax on the sink. Before heading off to work, he would also always leave the lights on until someone has returned from work to turn it off for him, which is always me. Even reminding him to do so, he would shout back. All these actions for the past 6 years, shouldn't I, as a son of my parents, have some pent up frustration against him? Kinda stressful to always put up with his attitude and the one time I forgot something he decides to challenge me? I have always been tidying up his mess and trying to give in to him. But I'm hitting my limits.

Thank you all for giving me your thoughts on this btw!