There are more anecdotes about Dijkstra in this collection of testimonials written by his friends, colleagues, and students: https://arxiv.org/abs/2104.03392.

These are some of my favorites:

From Tony Hoare:

They removed recursion from Algol 60, on the grounds of its alleged inefficiency. Edsger's answer was that recursion was a useful programming tool, and every workman should be allowed to fall in love with their tools.

From J.R. Rao:

He would repeatedly stress the importance of choosing words carefully: "If you have to use your hands, then there is something wrong with your words", he would say, adding "imagine there is a blind man in your audience, how would you speak?"

Over time, I came to learn and appreciate that Prof. Dijkstra's class was operating at two different planes. There was the lesson and then, the lesson within the lesson. At one level, the goal was to solve the presented problem. At the second and more richer meta-level was the approach for arriving at the solution.

Prof. Dijkstra taught us that in computing science, complexity comes for free; one has to work hard for simplicity.

From Alain J. Martin:

In his technical writing, he used language like a precision tool. For him, precision did not necessarily imply ease of reading, and he stated that the reader also had to make an effort to understand.

From Christian Lengauer:

Professionally, Edsger's impact on me is best summarized by his ATAC Rule 0: "Don't make a mess of it." It made me strive for simplicity in notation and modelling throughout my working life and take unpleasant complexity as an indication of a possible lack of comprehension.

I decided against writing with a fountain pen. He never took issue with this, except in a letter that he posted seven weeks before his death: "I hope you will overcome your resistance and learn how to fill a pen without soiling your fingers, or otherwise you are denying yourself one of the joys of life." These were his last written words to me.

From Lex Bijlsma:

A famous quote of EWD is the following: 'I mean, if 10 years from now, when you are doing something quick and dirty, you suddenly visualize that I am looking over your shoulders and say to yourself "Dijkstra would not have liked this", well, that would be enough immortality for me' (EWD1213). I can testify that this actually works.

From K. Mani Chandy:

When I write papers, even now, I still see Edsger over my shoulder going "Tsk! Tsk!" [...] I found that being less sloppy not only helped my readers understand what I had written, but most importantly, helped me from confusing myself.

From David Turner:

I have an invisible Edsger inside my head which looks over my shoulder when I am writing and quietly goes "Tut tut" if I write something that is muddled or not accurate. I don't always listen to that voice but know I should.

From J Strother Moore:

At faculty meetings when Edsger was not present it was common for someone to say "If Edsger were here he'd say such-and-such."

He came to work in the summer wearing a big Texas cowboy hat - they are made to keep you cool in the Texas sun. Often he would have on a cowboy's string tie. So from the waist up, he looked more Texan than I did. But he almost always wore shorts and sandals, which ruined the cowboy image completely.

From David Gries:

Edsger critiqued not the person but only what they said, and later one could drink a beer and laugh as if nothing happened. Technical differences and shortcomings should be treated this way.

From Maarten van Emden, edited for brevity:

Douglas Engelbart aroused Dijkstra's ire so much that he needed a whole page of vituperative prose to offload his emotions (EWD387). What has Engelbart done to provoke this outburst? One only has to refer to "Engelbart's Law", see Wikipedia. Its reasoning seems to run as follows: look at what mere printing has done as a tool for thought; the system demonstrated is so much more powerful than printing that it must quickly lead to Intellect Augmentation. This way Engelbart showed no appreciation for the rich culture developed over centuries. What makes printing a powerful tool for thought is mostly due to other things than technology. Much of the power of this culture comes from publishers and editors, who sniff out what is worth printing and hold back what is not. Another important component of this culture is provided by libraries and librarians. Much is due to scholarly societies, which started printing their proceedings and to commercial publishers, which created journals, each with their editorial board and unseen bevy of reviewers. Most of all it is due to the idea of a university.