One who will secretly take small amounts of marijuana from another; many times from a plastic baggy, but more recently from a small glass container.
I come home from work, check my stash and it keeps coming up light. I'm quite certain my unemployed roommate is a bag raider.
One who is thought to have been taking small amounts of weed from someone else's weed bag without the others knowledge.
"I think my new roommate may be a bag raider."