There's no proper context for this one. Cates Just wanted to write someone being evil for evil's sake.
Every year since David's birth, Thanos fucks with him on his birthday. It started with taking his blanket as baby and escalates from there. Sometimes they range from being just a dick to David, to other times killing off everyone but him at a frat party. The one constant in Dave's life is Thanos... well, except one year. His entire life keeps getting repeatably ruined by Thanos, which leaves him constantly with the question "why?" Thanos never answers until Dave thinks he finally figures out the reason. Then Thanos hits him with the truth.