1. Something, such as a program or a computer, that fails to work, or works in a remarkably clumsy manner. “This text editor won't let me make a file with a line longer than 80 characters! What a bagbiter!”
2. A person who has caused you some trouble, inadvertently or otherwise, typically by failing to program the computer properly. Synonyms: loser, cretin, chomper.
3. bite the bag vi. To fail in some manner. “The computer keeps crashing every five minutes.” “Yes, the disk controller is really biting the bag.”
The original loading of these terms was almost undoubtedly obscene, possibly referring to a douche bag or the scrotum (we have reports of “Bite the douche bag!” being used as a taunt at MIT 1970-1976, and we have another report that “Bite the bag!” was in common use at least as early as 1965), but in their current usage they have become almost completely sanitized.