When the enemy team plants a bomb on a door in Voidstar... While five of your teammates are over there.
When three Sentinels and two Guardians leap at you while you're on a fire pit in Huttball.
When Darth Baras Force charges at you.
... when you discover that your "Tank" is actually a sentinel who THINKS he's a tank.
Hah, I've actually tanked Hard Mode flashpoints on my Marauder, holding agro through sheer DPS and using Cloak of Pain whenever I can