I believe you only have the option of blowing yourself up when you are downed. So if someone lights you up and then comes in to finish you off with a melee, you can return the favor.
Just throwing in the
Dystopia-Mod here: Cortex Bomb - makes you blow up when your HP fall under 25. This actually allows you to use Quacko2's tactic.
You just need the Leg Boosters, the Cortex Bomb and an enemy willing to shoot you while in close proximity.
(However, if you get killed before you blow up, nothing happens. Which, again, is similar to BRINK. If you shoot a downed Operative, you don't have to get close so he couldn't kill you.)