One of my project managers has a bad habit of saying things like "It shouldn't take long" or "It should just be a case of doing...". Worse is when I overhear those words being delivered to our product stakeholders before I've even had a chance to evaluate the problem.
In a previous company our development team manager and lead engineer had a rather heated disagreement with some project managers about a work estimate he'd provided because they believed the Proof of Concept system written by another team would account for 80% of the final production ready product. There was profuse objection when told the PoC worked for a narrow set of use cases but the quality was such that none of it could be used in production. Egos were bruised and strops were had. Bad times.