They're all idiots. He's surrounded by them. Two loud, ranting idiots and one smiling, unbalanced idiot.
On an average day, Sanzo wants to punch Goku and Gojyo in the face about twice as often as he slaps them upside the head. (Contrary to popular belief, Sanzo does actually know the meaning of restraint. He even practices some sometimes.)
On the days he wants to punch Hakkai, they're usually too deep in shit for Sanzo to bother with exact numbers, but he knows it's a lot. So it evens out.
He doesn't know what he's done to deserve this cursed life, but he knows someone's got it in for him. Damn right he'll shoot the Buddha if they meet on the road - saddling Sanzo with this bunch, shooting is almost too merciful a fate.
Stick the Buddha in a jeep (that is sometimes a small white dragon) with these three and see how much the Buddha likes it.
Sanzo will be taking bets on how long it'll take the deity to take up smoking, cursing, and shooting stuff. If the idiots are lucky, those things will be enough of a distraction that the Buddha won't shoot them.
It's worked for Sanzo. So far.
The next stray kick, hungry whine, or too-cheerful laugh might be what push him over the edge.
What he is trying to figure out right now is why it hasn't already.
How many days since they left Chang'an? How many weeks and months of living with these three in his face every day, and he hasn't killed them yet?
How is he still heading west, always west, following the instructions of deities he'd rather ignore? How is he still doing it together with a polite mass murderer and a leering perv and a fucking monkey that's nothing but a loud stomach on legs?
He can't figure it out.
He can't make sense of it.
The only vaguely plausible explanation is that he has finally gone crazy.
Crazy enough that maybe he's not thoroughly miserable every hour of every day, even though he should be.
Crazy enough that their noise can drown out the sound of rain ringing in his ear, and their constant presence is making it hard to remember how to be lonely.
So crazy, in fact, that there are times when he catches himself thinking the word home, and imagining a jeep that is sometimes a small white dragon, and three idiots, all five of them on an endless journey to the west.