This was a regular occurrence over the summer with the late STN - IBZ. Let's be honest, it comes down to the quality of passengers that are carried and the fact that 9/10 times they were let on board already plastered...
.. but they pay the wages so apparently it's okay.
I never want to work an IBZ turn again. Great for the commission but that's about it.
EDIT - just read the above comments and yes, it usually comes down to the fact that they've been drinking the whole wait in the terminal and that they've smuggled their own alcohol on board and have been very successful in drinking it out of the C/C sight. Unfortunately OTP pressurises crew against offloading the passengers as the time taken for a bag search is unattractive to the company.