Suicide is a feature present in all of the Strike Force Heroes titles. It occurs when you do enough damage to yourself to bring your own health to 0. In the message list, the game will place the word "Suicide" in pink text, the method used in brackets, followed by the user who did it.
Getting caught in your own explosive area-of-effect and being caught outside the Environment boundaries can trigger the suicide.
The AI with launchers and the like are very prone to explosive-based suicides, as they might hit a nearby wall or platform while trying to aim for an enemy further away. They are also not immune to falling off the edge in maps such as Hijacked.
If in kill-based game modes such as Deathmatch, each suicide deducts a single point from your team. if you kill an enemy but suicide with the same shot, the net change is 0, so there will be no change in the score. It, however has no effect on other modes besides the fact you will not be able to play until you respawn again.
Be aware that if (very rarely) you killed killed by an ally's explosive, the game will deduct a point from your own score, though it will not count as a suicide.