And this proves he intended to commit suicide? Someone depressed enough to want to kill himself usually feels his life isn't worth living, not that other people aren't worth living with. His decision to commit suicide is based on his perception of the lack of value of his own life. Hinrich's statement is strange because he doesn't refer to his own life as not worth living. Instead, he denigrates other people as not being worth living with. So his statement could be interpreted as meaning he wanted to do away with those who weren't worth his living with.
I agree that this is odd wording. If indeed Hinrichs wrote this--and we have no proof he did--it seems to suggest that he had some beef with Cheema and friends (contrary to Cheema's contention they barely knew each other.) However, the attempted ammonium nitrate purchase alone argues against this being a merely personal issue.
My guess is that Hinrichs did not write that message. The subtle nuance of preposition in American idiom is the hardest to nail.
The authorities didn't release the full statement he left on his computer. Only the "kiss my ass" part. What did he say before the "kiss my ass" part? Enquiring minds want to know...
Plus, remember that according to other articles, they found packed bags in his apartment, and a road atlas on the front seat of his car. He was planning on making a road trip, also known as "bugging out after the bomb."