Deus Ex defeating Barret in under 30 seconds

Defeating Barret All you need:

a concussion grenade
5 or 6 Fragmentation mines (get them from DRB territory/ OMalleies apartment)
take cover as soon as the fight starts throw a concussion grenade followed by 5 frag mines - that should do it even on hard

actually its closer to 20 seconds looking at it :)