I have this sort of discussion, at minimum, three times a week (we're in-house developers). Very often the project scope isn't even defined and upstream dependencies are known to be critically lacking and will need to be augmented to even perform the work. Yet we're always pressured for dates and the caveats given are immediately forgotten and almost never communicated.

The biggest pet peeve is when I give an estimate such as "I don't currently see a reason why we can't deliver X by the end of next week, assuming no other priorities come up." Of course something more important comes up in the mean time and I get scolded in a large meeting with a statement such as "You promised me I'd have X by Friday!" — this is especially infuriating when it is the PM's other project that is the higher priority interruption.