'To Bump' something is to snort a drug. Usually Ketamine but can be speed or coke.
To have 'A Bump' is to snort a small, conveniant amount of the above substances. Usually on the corner of a credit card or a small line snorted from your hand or otherwise.
At home: "Let's 'bump' a some fat line's of K and get into a K-Hole."
At a Club: "Here, have 'a bump' offa this bankcard."