Bolded the important part. Big Bang is an aoe effect - he doesn't target you and cast it on you; it just affects anyone who's not in a black hole - and since Spell Deflection doesn't work on any other such (as far as I'm aware) it shouldn't work for BB either.

Rune of Repulsion is bad for DKs Always has been.

All of the following are better: Valor Medal of the First War, the Black Heart, the Furnace Stone, heck, the last time I checked, Repelling Charge even delivered more avoidance (the added damage mitigation boost to IBF ain't bad either).

Here's a parse of last night's raid for those interested in my build's performance - WWS / WMO

It's not ideal, there really isn't an example of me tanking solo or all the way through a fight. I'm DPSing on XT and Auriya I'm only briefly picking up the adds. I'll post some more as the week goes on. We ran a solid 10man AC, which no one caught a log of. And for anyone interested in the multiple deaths on Beasts, we had a pretty frightening healing situation that fight, and I was more or less sacrificed. One healer in tank gear, one dc'd, and I think one or two might have died as the fight progressed. A pretty sad testament to the ease of the encounters that we still downed them.

There is a point I'd like to make though, especially to anyone testing the build - it relies heavily on cooldown management and proactive mitigation. Gormok's killed me fairly regularly and consistently late into the fight because of his ramping damage, knockdown (which, I think, prevents dodge or parry), and impales. While I'm tempted to blame healers, I should have survived through like our other tank, but didn't save IBF for the right time.

Edit: It's not WWS, but here's the breakdown and DPS data from recount after the AC10 that I tanked.
Northrend Beasts:

Jaraxxus:

DnD is higher threat per second than anything you're going to get from an extra blood tap.

For me, on large AOE pulls, I do DND, IT, PS, Pest, Blood Tap, BB, and then start into my normal rotation (DS, HS, HS, DS, DS, HS, HS) since I do not use DRM. I have Morbidity 3/3, so shortly after, I can cast another DND if it is really needed, and my threat never gets beat. What is your hit rating at? Maybe you're just missing spell hits too much and not getting the threat you need out there.

Your spec seems a little off. Why Blood Worms - they give you no threat, and you shouldn't need the healing from them. Mark of Blood is very situational, and seems like a wasted point as well. DRW got nerfed hard this patch, and if I remember right, also doesn't give it's threat to you, not to mention it is more of a DPS talent. You also don't really need 3/3 in Scent of Blood - you generate more than enough RP with 2/3 in it. So that's 6 points you can reassign elsewhere for better threat and AOE abilities. Personally I have 3/3 in Spell Deflection (testing it's effectiveness with the Parry normalization numbers, so far, very promising) and 3/3 in Morbidity to help with AOE tanking so my threat never is an issue on large groups of targets.

Right now, I average about 2300 DPS on any given heroic, including heroic ToC. As a tank. Never have threat issues. Every healer I've had has said that "healing you was a snooze". So might want to look at tweaking your spec some?