It's only taken me two decades but I've worked out why I've never liked people using the term "grok", despite being a big nerd who's the right age to have read that Heinlein novel.
Using it is a way of reinforcing your sense of being part of a special group, one which has a privileged relationship to the process of learning: you don't merely understand things, you have access to galaxy-brain superthoughts about them, which you can't even refer to using ordinary words.
This isn't healthy. It's using language to build walls, not bridges between people with different talents and specialisations, or who don't come from the same pool of in-jokes as you do.
And it wasn't even a very good novel.