I don't tank. I don't heal. Among other things, my Chinese isn't up to it. Still, every once in a while, something happens. It may be that I queue for a scenario and find we need someone to soak or heal damage. It may be that the tank d/c's or goes down to a bad pull. In those moments, one can drop group or one can step up and try to fill the gap. Recently, I've had some good fun with that kind of moment.
For example, I was with an otherwise good group when the healer dropped out. Not surprisingly, I see the message pop up about "xiao D" and guess they want me to switch to Resto. Nope, I'm the other druid, I'm spec'd Feral and Guardian; trees are there for me to sharpen my claws, you want me to turn into one? No way! Still, the wait can be boring and the DK tank decided to see if he could pull some of the mobs. In a complete violation of min/max-ing, wearing not one speck of caster gear, I decided that I should try to heal him (the other DPS was a Hunter). Granted, Cenarion Ward is OP at TBC levels and healing a Blood spec'd DK isn't exactly rocket science, but it amused me. Sometimes it is nice to step outside of the 'optimal' play style.
What are some of your "fit hit the shan" moments?