Why would anyone EVER do that?

So since I am a high school chemistry teacher I get some pretty weird things happening in my classroom. But yesterday I had an experience that left me wondering, why would anyone ever do that? So the incident happened during 3rd period (my class from non-heaven) , and we were cleaning up a lab on concentration. I was in the front of the classroom and one of my students said that another student had thrown salt all over their lab desk. So I went to go investigate the situation, and it turns out that he had, so I told him that he needed to clean it up. When I was done talking to that student I looked around the rest of the lab and there was salt EVERYWHERE! So I asked some students what happened and they told me that same student (who shall remain nameless) had gone on a salt throwing rampage and had thrown salt all over the lab. So I had another talk with the student and he looked at me like I was crazy to even get frustrated about it. Which left me a little mad, but it happens. So sorry if this was just me venting my frustrations, but really can anyone think about why he would do that in the first place? The only reason that I can think of is that he just wanted to make people mad. Why woud you do that?
Oh...and if you really want to make a pregnant teacher mad inform her that she is mad and frustrated because she is pregnant "Oh..she is just mad because she is pregnant," is the exact quote . Ahhh....gotta love high school students!