This originally meant, literally, a bag to carry a device that women cleansed their vaginas with. It's now used as an insult, mostly against males, similar to calling them a jerk, bastard, etc. What the insult specifically implies seems to depend on regional vernacular.
"John, you're such a deuche bag for cheating on me."
A bag used for your vaginal crevece... to clean it out and such. Used sometimes when umpires at softball games are idiots and dont know what they are doing.
I heard plain and clear with my own two ears out of one of your girls mouths... that the umpire was a deuchbag.. NOW I GOT ONE QUESTION FOR YALL, WHATS A DEUCHEBAG, HOW DO YOU INSERT A DEUCHBAG, WHERE CAN I LOCATE AND INSERT A DEUCHEBAG?