To report (a person) to someone in authority for a wrongdoing.
I’ll dob on you if you break in.
To do one's share; to contribute.
We all dobbed in for a gift when he retired.
To nominate a person, often in their absence, for an unpleasant task.
I arrived just after the meeting had started and found myself dobbed in to take the minutes.
To play truant
(sometimes humorous) In the scouting movement, to chant dob to indicate that one will do one's best to follow the scouting laws.