Been there, done that, got the T-shirt.

My horror story is management/marketing saying "we want SuperProduct 3.5 to be released in October, with this feature set" ... without actually sizing how long each feature would take to implement.

And guess what? We missed the deadline(s) ... and who looked bad? And it doesn't help to complain about it at the time, because you just end up with a reputation of being difficult/negative/not "can-do", etc.