There are multiple ways to deal with this cheese in 2v2, I'll list the ones I have had the most success with.
- If possible, both wall off or almost wall off (leaving a one gap with a hold position zealot would be what I consider almost walled off)
- If not possible, you can actually try to fend it off by pooling most of your workers together until you have your own combat units. One base worth of workers holds off 6 lings...two base worth can hold off 12 lings. This can be a bit tricky to do depending on the map, and you have to be careful to not spend too much time chasing the zerglings (if they don't fight you) instead of mining.
- If you are quick enough in spotting it/pumping units and/or defenses, simply sending units as you produce them can sometimes hold this off.
- In the case of a zerg/protoss pair, you can try sacrificing the zerg, walling in the toss, and getting a quick void ray up. Their economy will be so weak and zerg anti-air comes so late that a single void ray (or at most 2) will generally suffice to kill one if not both of them.
Some people suggest spine crawlers or other base defenses, but I haven't had much luck with these. They aren't up in time and they will usually simply focus fire them while they are building, leaving you down money and drones with no real gain. Any reasonable player will also do things like focus fire your hatch if you try to run around stalling for your partner to arrive, and 12 lings take down a hatch fairly quickly.
First off, let me start by saying: There is nothing wrong with Carriers.
Though they haven't seen the same revival that Battle Cruisers have under Terran, Carriers remain a very viable late game unit. Even in a world of "Hard Counters" Carriers do an enormous amount of damage and require very micro to beat. For players invested in heavy ground forces Carriers make a very nice addition and force an opponent to "split" his strategy between disparate units. While many people might point out the effectiveness of Vikings, Void Rays and Corruptors against Carriers, you have to keep in mind: All those units are effective against Colossus and those still make many appearances.
The largest problem with Carriers is they are often overshadowed by Void Rays. Void Rays are a very powerful unit against Armored and once charged. By comparison Carriers have neither of those drawbacks and are only more expensive. Finally, while many people will tell you that Carriers are countered by good micro, this is also true for EVERY OTHER UNIT IN THE GAME. The only difference is that Carriers are more effective against bad micro.
Now you discussed Carrier Rushes, and what I am about to say could apply to any type of rush: A Rush is not necessarily a Cheese. You should not use the term Rush pejoratively.
Technically going 2 Gate is a kind of rush. A rush just means quickly getting to something, and is frequently used as a technique to counter more Macro intensive play. Since many players play a Macro intensive play, a rush is a very good strategy. The trap your friend is falling into is that he is surprised by the sudden force and is using the term rush to dismiss it.
"Oh you didn't really work for that, you just rushed it."
This is actually a mistake in terminology. What he means to say is: you're doing an all in gamble on Carriers and if they failed you'd be screwed.
All in play is often considered boarder line cheesy because you are often unable to recover. However, since the goal is to do more damage to your opponent than you are doing to yourself, a very good timing all in, is an incredible effective strategy. Since an all in does not rely on lucky or bad play from your opponent, it is not nearly as cheesy as something like a proxy Rax. As a result, most All Ins are more moves of desperation than cheese.
Whether or not you consider All In play to be cheesy, a Rush is not by definition a cheese and you shouldn't feel bad about it. Even if you had Rushed Carriers (which it sounds you hadn't), that would be an interesting new build, not some sort of gambit play. So build them at your leisure.
And do try to enjoy yourself while playing Starcraft 2.
Best Answer
Most of the advice to stop Nydus worms applies in general. First of all, you should be keeping an eye on your base no matter which race you are facing, and regardless of whether or not you have scouted a Nydus Network in the Zerg's base. All races have ways of getting units into the back of your base without going up the ramp. Medivacs, proxy pylons, overlords with ventral sacs, warp prisms, blink stalkers, colossi, reapers, etc, not to mention pretty much any air unit.
Denying vision to the zerg player by harassing overlords should be done in general, not just to stop worms.
To help detect the nydus worm (and all other threats mentioned in previous bullet), spread buildings out in your base, so you have vision everywhere. Terrans can spread supply depots, protoss have pylons, and zerg have creep tumours, or overlords to spread around.
Learn the sound a nydus worm makes when it completes. Sadly for us zerg players, the nydus worm announces itself to all players with a loud scream, similar to how everyone hears "nuke launch detected". On the plus side (for us), it only screams as it is finishing. This won't help you stop the worm, but it will alert you that you should be looking for the worm to make sure it's not in your base, or if it is, mobilize some troops to defend.
In team games, consider using the team colors option for the minimap, so your units are green and your opponents are red. This will make the nydus worm stand out in your minimap more than if you are orange and your opponent is yellow, or some other combo of similar colors.
Worms don't have a lot of HP, even when they complete. When they are building, a handful of units can kill it before it completes. I just did a quick test; 3 marines starting to shoot as soon as the worm reaches 50% done can kill it just after it finishes, enough time for only a few units to get out.
Remember that each worm costs the zerg player 100 minerals and 100 precious gas. Each time you kill one before it completes, the zerg is behind on resources. They can also only be building one at a time. (specifically, one per Nydus Network)