Linus is blunt, like myself and many other Finns, and used to cuss out those that offered him badly done work, or were plain wrong but refused to acknowledge it.
I still do, with vigor, because I get so angry when someone offers work product they clearly didn't put any effort into, or even thought about at all. They deserve a cussing, in my opinion. It is different when people have limited capability; having the capability but not giving a toss and being wrong, and refusing to admit it, is definitely worth a hard cussing in my book.
As to him being a dick.. Well, one of his favourite party tricks at university parties was to have his then girlfriend, now wife, Tove, show some moves by throwing him around.
Those that say he is a dick mean he isn't as socially graceful and aware as they think he should be.
Because he has tried to become much more so in the last decade or so, his own work quality has fallen.
(My favourite examples are some of the subsystem inanities he's let into Linux, like the input event ioctl() stuff "replacing" the standard read()/write() interface, without bringing anything positive, just complicating simple things -- and the patches claim it is for the good, because sometime in the future, they might wish to change this interface. It hasn't, except for the ioctl inanity, since 2001 or so.)
In his own words, his biggest responsibility is to be able to say No to stuff.