I play both a warlock and a paladin tank in pve myself, so I know what its like to tank.
I usually group up with 3 guildies when I'm on my warlock (of which 2 are dps and one is a healing, this means we're only pugging a tank).
All 4 of us are quite geared (my warlock is in 226/232 gear, and the others are in 232+) so we pack quite a punch, add to that that the 4 of us are on skype together usually.
Usually everything goes smooth and the tank just keeps chainpulling. However, sometimes, when the tank is slacking, we decide to take matters into our own hands. Thats how we found out that my warlock in furious gear can tank heroic nexus. All of it. We've already made a couple of teri-bad tanks leave because they felt useless xD.
Nothing says 'you suck' more than a dps doing your job, and being better at it too.
Its not because we're elitist or anything (hell, apart from my paladin tank we're all in full pvp gear), but honestly, there's no need for 10-30 second breaks in between pulls. We know we can handle it without a tank on 99% of the pulls, thats why we pull.