Would I be justified in killing them when they use it this way, or should the punishment be lighter?

It sounds totally wrong to me, too. Perhaps there are alternatives to killing them, though. Maybe bring in some Merle Haggard cds? Or perhaps sing something, yourself? Oh, or just bring in that brand new baby right around feeding time (or diaper changing time).

Do you think perhaps your coworkers are simply referring to unpaid vacation time?