Tell someone something is going to take about an hour and a half

20 minutes later they get in my face bitching

Hold on... here's what's going to happen.

I'm going to take a deep breath. I'm going to nod. I'm going to bypass the obvious move here. You just wasted 5 minutes of my life yelling at a very inconvenient time. So I'm going to take 10 minutes longer than the previously quoted time. I'm not sure why it took your brain ~ 20 minutes to process after the fact. But now you have an extra 10 minutes to think about it. Please step out of my face or I'll just double it. K thnx bye.