Fun fact, you can play tough too.
Manager: We (meaning you) need to do task A. How long will it take?
Me: Task A will take X days to do.
Manager: That seems awful long.
Me: How long do you think it should take?
Manager: It surely could not take any longer than Y days.
Me: Ok, which features are you willing to remove to make it fit in this timeframe?
It's surprisingly effective, especially with a bit of seniority.