I actually have that achievment, but it makes no sense to me... did I play against a RockStar developer in an online match and kill him? That's really odd.

Yeah, there are some pretty dumb achievments out there... I think the hardest one for me to get so far is "single handedly kill a tank" in Left 4 Dead.  It's hard enough for 4 people to survive a tank, I can't imagine getting it without cheating in versus mode.

It's entirely possible and quite easy, the only hard part is you're going to need to kill your teammates (unless you decide to play single player mode than that's easy =). Just start a game on expert, when you hear the tank music shoot your mates with an auto shottie they go down in 1 hit, make sure you have a single molotov on you, throw the molotov on the tank and run, make sure he doesn't hit you with the giant rock.

Another way is to play Blood Harvest last level go out the window in the room in front of the bathroom after you radio in, be careful you don't fall off because the edge is really small, make sure you have a lot of ammo and if you get lucky the tank will glitch and get stuck. If you're not lucky he'll just fall off and you have to repeat the process.

edit. Also remembered one more method, it requires a starting safehouse with a door that can be closed not in an open area. When the tank comes run back to the safehouse shut the door, make sure the tank doesn't throw a rock on the safehouse door cause it'll break. When the tank gets next to the door you have to move up against the door and it won't break.

It's simple to do in No Mercy on the rooftop.

After the first two waves of zombies are killed have everyone immediately run the area where the mini gun is.  On the left side there's a ledge going along the side.  Have everyone carefully get onto that ledge (no big deal if you fall, just takes time to get back there) and then viola!  The tanks are simple.

They can still throw rocks at you, but no normal zombies, boomers, and tanks can't really hurt you there.  You can still get snagged by a smoker or hunter, but that shouldn't be too much of a problem.  Just pick the person that needs the achievement and let them kill the tank.  You pretty much have all day.

(this strategy makes No Mercy rooftop simple on Expert )

I think I know what you mean... picture this to make sure I am right, we are facing the gun and then do an about face and the building right in front of you (the A/C unit are on top of it) get on that ledge on the left side?  Actually, if that is what you are saying, I can see why that would be such a great strategy.

Sweet, thanks for the tip... now I just gotta get someone to do it with!  Most of my clan-mates are playing COD:WaW, but I know one of my friends is still playing (him and I are boycotting the new COD, tired of the WWII genre)

Which brings up another point, of all the games I've played, there are some really horrible players in this game.  I always get stuck with at least one dude who thinks he's Rambo and runs off by himself, which of course in this game leads to everyone's death. 

Anyway, thanks again, great tip!

Rambo's are always annoying but I've only really encountered one and he didn't stick around for too long thankfully.

I actually had a pretty bad group for the first time last night.  We were playing Blood Harvest on expert and it started out good.  Everyone had mics at least.  And then we left the first safe house.

Three of us bunch up and start killing some of the zombies in the distance.  A few come running at us and then one genius decides to run in front of us so he can get in their face with the shotgun.  He steps in front of all three of us and just immediately goes down.  He called us a bunch of fucking noobs and then quit.

The rest was going decently.  One of the guys never really got the whole you have to crouch if you're in front thing but it was fun.  We had a lot of excellent finishes and just had an all around good time even though there were only three of us (we saw the douche try to join a few times and then instantly quit when he saw it was us).

We then got to the finale, made our plan, and then got slaughtered.  It was just one of those times we had a bad start and things just kept going down.  No big deal, it happens.

So we restart and one guy pretends to disconnect.  The second the guy leaves the other guy then pulls the same act.  Twats.

That really sucks man, I know exactly how you feel.  The other night I was playing with 3 new guys who were playing for the first time... no problem, everybody has to start somewhere.

So I'm showing these guys where to go, hide, etc, etc, on expert, and I manage to get all 3 of these guys to stage 5 on the hospital building, and one guy says, "hey man Nick just got on line... sorry dude you gotta go"

Boom, I was booted from the game just like that... I spent about 2 hours getting these guys to the roof, holding their hands, teaching them how to play, and what thanks go I get?  Booted on the final level.  I'll never do that again.  That was a huge waste of two hours of my life.