Aizawa became an insomiac during high school. He ended up dedicating a lot of his sleep time to his studies, but also making sure his classmates weren't over working themselves. By graduation it's practically tradition that he passes out on Mic's couch and everyone buys him a cake saying "Thanks For Everything, We Love You Ultimate Tired Mom Friend".
This is so cute. Aizawa probably wouldn’t know what to do at first with all the attention. Saying it wasn’t necessary and they shouldn’t have gone through the effort, he was just doing what needed to be done. Of course, everyone would insist and eventually he would budge. Showing his appreciation even though he wasn’t expecting the thanks.