In Modern Warfare 2, does your kill streak end when you get killed by a team mate in hard-core, or only when you get killed by an enemy?
Regardless of the type of death, your killstreak will end (suicide, enemy kill, teamkill). However, this will not count as a death in the standings, nor will it affect team standings. It will just give the offending player -100 points (or whatever -1 kill is worth in points in that game). Hardcore is best suited if you all have headsets, since you won't know where everyone is, and so communication will cut down on "freakout kills" when two teammates turn the corner and react before they see it is a friendly.