Sans, psychology is very important, and for an oppressed and downtrodden population like the monsters it would have done a lot. Many monsters we met seem neurotic, some just seem very eccentric but others deeply "disturbed" in some ways. You yourself have a lot of repressed anger, we all remember the "drunken outbreak" you had. That is something that should be treated. Sans, alcohol is known to loosen inhibitions and make you more likely to actually say what's on your mind.

You do have anger issues. You repress them but that doesn't mean they are gone. And when they come out you tend to explode and regret it afterwards because it shows a side of yourself you don't like to admit exists. And when confronted with an option you don't like you tend to storm off like an angry teenager to their room, slamming the door along the way. Only your "door" is a dimensional portal. Reasonable anger? You really are quite the comedian.

Sans you are holding a child who is terrified of you because of your anger. He believes you'll turn on him once he fails to meet your expectations. You have yet to actually speak to him about accidentally frightening him. Dude you called Frisk, and I quote, a "fucking disgusting human." If that's not anger issues then I don't know what is.