ENTps and "your mother" jokes

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The scenario: I am in my LSE friends living room. He is in the kitchen. His mother died a few years ago. His mobile phone that is on the table next to me starts to ring, displaying the name of the caller. My frined shouts through to me.

Him: Who is it?
Me: Your mum
(pause)
Me: hmmm perhaps not the most appropriate joke. (realising what I had done)
Him: Yes I was going to say that would have been impressive
Me: Yes

lol.. that joke was in some Hugh Grant movie. Something like..

Her: Who's at the door honey?
Him: Your mom!
Her: She died 5 years ago!
Him: Yeah I know, it's really weird!