1. To bail out of an event of any gravity whatsoever
This is usually school assemblies, interviews, tests or physics exams.
2.Also, to "pull a jeff" may refer to any act of appearing sleepy or fatigued, or to leave school early (ie lunchtime) to go home and sleep.
dude1: what do we have next man?
dude1: /pulls a jeff
dude1: man you look baddddd, you should pull a jeff