He specced WHAT?! (or "how to be nice to your PUG tank")

I'm fairly certain that I managed to scare off our tank in FC today. Oh - it wasn't anything overly aggressive. He was specced for 2H (sometimes a valid build) at level 28 with a group consisting primarily of level 28s with me, a level 33 chloro.
The first pull went reasonably well, although I noticed his health was moving more than I would have preferred. As a chloro I'm severely limited in what I can kick out as an insta-heal - I can keep you up as long as you can survive for 6s (about the amount of time it takes for me to cast a few offensive spells, which are the primary means of healing).
Subsequent pulls (all 3 of them) were painfully bad. He died in every one of them before I could get a single nuke off.
In an attempt to bring some sanity to the PUG party I asked if he had a build with higher mitigation, or maybe some gear with higher armor. He dropped group without saying a word and went on his way. I felt a little bad - I didn't mean to frighten him off, but it had become obvious to me that it just wasn't going to happen with him as our tank in that spec.
Is there a better way to handle a situation like that? I could have just let us continue until somebody else got frustrated and dropped group, but that didn't seem like a smart thing to do. Any suggestions?

Tone is often hard to convey, especially in a purely textual environment (you didn't mention vent, anyway). The best you can do is try to stick to neutral, non-aggressive words, and be as precise in choosing them as you can in the rush of trying to keep a typed conversation doing something akin to flowing. ;-) You might start with something like "let's hold a minute and see if we can figure out a way to improve this situation". Then explain what you did above (I've found a whole lot of folks don't understand how chloros heal, especially if they haven't been healed by one before). Tell him that for this to work, he really needs to be able to survive around 6 sec from one full heal till the next. Then ask your question about a mitigation build or some different gear. If he bolts at that point, nothing you can do. Odds are, this was his first time in a dungeon, he was frightened about looking bad, and had no clue what you were talking about. Not much you can do about that except be kind and offer to help. But yeah, as soon as you know it's not working, you're better off to try to figure out how to remedy it than to let it slide. Just try to make it clear you're not accusatory or pointing fingers. Offer to help (with any info you know that might help him be better at his role), and the rest is up to him.

I'm not saying it can't work, especially at lower levels, and I know right or wrong isn't really the point of the question but it's going to be REALLY tough to pull off tanking with a two-hander. You're giving up a large amount of mitigation in the form of blocking and armor and the only real benefit you're getting is more damage and maybe a few points of parry. In my head I'm trying to figure what possible spec you could use to justify on paper tanking without a shield. I'm drawing a blank. There are a few finisher moves that might help, but it seems really unlikely to be as effective as a "traditional" sword and board. (The only thing that comes to mind is an ability available in Paragon at 20 that raises your parry by 75% for 10 seconds, and that has a 30 second cooldown) The fact that you didn't instantly go for the votekick speaks volumes for your intent. Waiting for 3 trash pulls that resulted in death is ... well, I'd say it could be one of those acts of saintlike patience. I'm assuming that this was a PUG group from the LFG tool. In the situation you described, I think it's legitimate to question the tank's viability in the kind of general terms you describe. I'm assuming you were diplomatic, and it doesn't sound like there was much debate on the subject. Perhaps he realized that even with a perfectly valid avoidance build that works great for soloing doesn't draw AE aggro quickly enough in a dungeon group.

Two-handers are absolute fail for tanking at this time. Their mitigation is minimal at best and the only real mitigation is parry and that's capped at some stupidly low level apparently. When your doing low level instances you really need a high mitigation build. It's more or less a guy that doesn't understand the mechanics or queued as a tank while he is dps geared. You can do it in experts now if you have a strong healers and the fight isn't very burst orientated. I used my 2hander on Gronik in expert CC yesterday and it worked out okay. Don't be worried about scaring him off stuff like that happens. Maybe he was just embarrassed. Hell I remember in WoW when I was tanking in a random PuG. I asked for the dps to wait for 5 seconds before initiating so I could maintaining aggro...Two DPS left while shouting insults at me. Just keep doing what your doing mate, sometimes you can find some 'gem' unguilded players to invite :D

It sounds like you were polite and simply trying to help the group be successful. I remember I had some troubles tanking for a bit in WoW. My stance was to generally assume the person was trying to be helpful as long as they did not throw in any negative comments. I agree with Tetharel though, tone is hard to convey. Perhaps emotes to help: "Trinak is trying to be helpful." vs "Trinak thinks your a noob." would certainly help convey different tones.

All in all the comments are about what I expected - just wanted to be sure that I hadn't broken some unspoken MMO code that I was unaware of. My takeaway is to first explain what a chloro healer does, then fall back to exactly what I did if problems continue. If you're having trouble on trash pulls something's gotta change.