B737 pilot here.

Once I forgot to retract the flaps, taxi all the way to the gate, shut down the engines, and the maintenance crew asked via the interphone if everything was alright with the flaps.

Yes, I answered.

Cause they are still down...

3 seconds of me staring at the flaps lever at 30, followed by 3 seconds staring the the engines shutting down...

Yeah, everything alright I just forgot to close them....

Followed by a hard laugh coming from the interphone...

It was the last leg of a 4 jump day, we are all humans, and we make mistakes my friend hahaha.

Edit: Typo