spoilers ....Why would Kevin???

I think he said something like "you don't kill the audience"

I don't think that he ever really loved his dad, but acting like he did caused his father to question Eva's assessment of Kevin, and caused a rift in the relationship between dad and mom, which kevin seemed to enjoy.

He killed him because... well, he was a psychopath, and any affection he showed towards him was just that ; a show. A facade. As someone in another thread suggested, he also possibly had an Oedipus complex where he wanted to kill his father and have sex with his mother. The scene where his mother catches him masturbating and he looks at her and continues to masturbate , plus the fact that he actually does kill his father , show evidence of that.

Maybe because in the morning of the murders, the father was having a giggle with the daughter and that ticked Kevin off?

1.- He killed them to destroy and break his mother psychologically forever.
2.- Other mass murderers had done the same before their public massacres. Charles Whitman being the classic one. Some other school massacre killers had done it as well,but I dont remember their names. It's basically to kill their own identities and history. Most of the time those are suicidal/suicide by cop adventures

I didn't get that "he adored dad" or that they were "best friends".....it was clearly an act to piss off and hurt mom.
Everything was about the mother, hurting her, pushing her, goading her, shocking her etc. Dad and sis were simply tools to use, not people to care about.

Spot on! I mean damn how in the hell did you not grasp that from the movie.

It is either a Lychee fruit unpeeled or Rambutan, which is another Asian type fruit that looks similar. Rambutan's have a reddish curly type of outside shell type of skin and a Lychee looks similar but doesn't have as much of a curly skin. They both look the same on the inside and have a pencil eraser sized hard seed/nut at the center of the grape textured fruit. It was definitely in reference to the girls eye, as they were talking about him protecting her at school (which he said NO to, in so many words). Also his mother said that he didn't like those before, and he makes a snide remark about that to counter his parents. As a trained professional, everything he shows is either early stage sociopathy, along with borderline personality disorder. He has no apathy toward people, they are just things to "play" with. As well as a clinical Flat Affect - where he gets neither joy or sadness from any experience. Things are done to just do them because it is forced (eat a meal with the family) or it is illegal not to do (like
go to school). Some will say that this is a part of schizophrenia, or a schizophreniform disorder; they would be correct in my opinion. They try knew things, to try to get an emotional response from either themselves or those around them (be it good or bad), but their brains don't register properly, and they act as though putting someone's eye out is the same as playing a game or watching a movie with that person.