So I run a weekly D&D game in a homebrew world and I've been having a problem with a player. He regularly tells the other PCs that their plans are stupid (which in his own defense, their plans are usually really stupid, stuff like explaining to the town guard how they broke into a local church and killed several people only to find out the priest was evil, however they did this without any proof... after being known around town as drunkards and troublemakers). Anyway to make a long story even longer he refuses to be around the party anymore, he hides from them and won't go on adventures. They're currently on their way across country to the capital of a new land and he's moving in the same general way as them and even took a boat with them, however he stated that he was only on the same boat as them by chance and would again ditch them when they got to the capital.

So what do you all think? a few of the players want him gone, but since he is a friend I don't really want to just toss him out of the game... So i'm not really sure what to do...

Any help would be appreciated.

Is your friend having fun? Are the other players having fun? From what you've written, I suspect the answer to both questions is "no." Given that the cardinal rule of gaming is "Thou shalt have fun," your options at this point are fairly limited.

1) Talk to your friend about this in private. Ask him to hang back after a session, lay your concerns on the table, and see if he's willing to modify his behavior. Remember, do this privately, not in front of the group, so that he'll be less inclined to go on the defensive.

2) Talk to the other players without your friend around. See if you can pinpoint the cause of the subpar planning. It sounds like your friend is taking the game much more seriously than the other players; sometimes that's fixable, sometimes it isn't. If the other players are only in it for a laugh, then you probably will not resolve this to everyone's satisfaction. Either your friend will leave the group, or everyone else will.

3) Apply in-game consequences. The town guard doesn't believe their half-assed story about the evil priest and throws them all in prison. Either turn the game into a prison campaign or declare that the end and have them reroll. The last option is bound to piss several people off.

The friend is the type to always complain about everything, no matter how good it is, and as for the consequences they do have them. In my previous example it was only some quick work by the groups face that the party just got run out of town instead of arrested. Since he managed to convince the city watch that the 2 people making the claim were actually raving lunatics hell bent on wasting the city watch's time and that none of that had actually happened.

The as for the question about fun the other players have a great time, and even tried to get the ditcher back into their game by telling him (After he had abandoned the adventure to rescue one of them who'd been captured by an evil cleric to be part of his newest batch of undead) that it was water under the bridge as long as he didn't do it again. He responded with "I may do it again if it seems prudent, and judging by how wounded you all are, i think it was the correct choice after all." so they told him to bugger off.

Sounds like your problem is well on its way to resolving itself.

[edit] Actually, something just occurred to me. Is he complaining in-character or out of character? If he's just playing his character, that's much more easily fixable than if he's talking as himself.

Both, he complains in character that they're all dumb and should just listen to him and shut up... then if they don't, he complains out of character that they're all dumb and he won't have any part of it then his character decides to run away from the adventure.

I know some people that would pay handsomely for that kind of abuse.

No offense, brother, but it seems to me that your friend's being kind of a dick. Based on what you've written, it seems like he's the one spoiling the game for the whole group, and that's just not kosher. The question is, do you let it ride and accept the possibility that he will drive an irreparable wedge into the group, or (and this is the more responsible option) suck it up and kick him to the curb? As DM, your responsibility is to the entire group. If your buddy refuses to play nice with others, all you can do is cut him loose.