The most offensive (to me) was a deadline that government regulations said was 3 years away (EFast2! Due 2009!). The mismanagers involved would not let us start working on meeting those requirements until less than 1 year remained. The product involved went from having 60% market share to under 25%. If they had not been purchased by a large conglomerate, they would have gone out of business from this. All the devs quit. The execs who created the crisis were fired. Some devs were rehired, about half would never go back no matter how much they were paid.
Where I work, we affectionately refer to this as “the dumpster fire” of priorities. I’m lucky that we also work together to both recognize and rectify the dumpster fire blazing out of control.
I've worked for too many managers where either everything, or too many things were urgent too frequently .. without any urgency gradient to differentiate.