When talking about "a waste of time", there are many things that could be seen as that. The most general way of wasting time is by not being productive and jusy laying around doing nothing, but I have a more,personal, subject to talk about.
So there was this guy called Mario. He came in our class in the 2nd semester of 6th grade, and he was this really small boy, not even 1.60 meteres, quite skinny too. Everyone was awestruck by how tiny the dude was, but luckily no one was mocking or bullying him about it. I tried to be friendly and make him feel welcome, doing things such as chatting with him during breaks, sharing my food with him, and helping him out with homework. I was among the first people to be friends with him, and I actually felt good that I made a new buddy. At that point, I had full trust in the kid, he seemed pretty laid-back and chill. I don't think he had any manipulative or bad intentions by that point, he seemed to actually enjoy my company. But he quickly noticed one of my key traits during those years, that being my intelligence. I was pretty much text-book nerd as far as my class went, being the only one of the boys who actually got good grades. He took advantage of my kind nature by asking more and more for help on his homework, even on the easiest of things, and even just straight up make me do his whole homework for him. Middle-school me thought that me doing this for him was just what friends do for each other, but he seemed to grow more distant as time passed and he made more friends. I still spent time with him, but it wasn't as fun, he just seemed different. He still would ask for help by text when I was home, but there could be days at school where he would totally ignore me. I grew more and more frustrtated by him, thinking I am the one doing something wrong if he doesn't want to be around me. Though, as I was approaching the end of 8th grade and the end of middle school, my frustration turned into disappointement, as my doubts about his manipulative behavior were confirmed true by me figuring it out, plus some of his friends being honest with me.
Not only was I disappointed by him, but I was also disappinted by myself. How did I not observe this earlier? All that time I spent with him, was he really my friend? Was I just his robot, ready to help him with whatever command he needs? I felt like my entire friendship with him lead to nothing, and him as a person was a waste of time for me. However, part of me believes that he was not always like this. When he first got in the class, when he wasn't aware of how well I was doing in class, he seemed to actually like me, so perhaps someone influenced him for how he turned out. He is the reason I kind of lost trust in people, but, my old friends, plus some new ones I made help me heal from that psychological damage. And who knows, maybe he now knows what he did was wrong, but for all I know now, my interactions with him were just a waste of time for me that I want to forget and move on from.