I have heard a Rav say that if someone is “metza’er” another jew by davening an abnormally long SE & thereby “locking” him in place – the entire SE is a “mitzva haba b’aveira”.
What constitutes a long SE? I am a very slow davener and shuls are often half way through chazaras hashatz when I finish.
When I was in 3rd grade, I was davening SE. When I finished (much after my class), one of my friends ridiculed me for taking so long. I made up an excuse about having to restart, but it took me a long time to daven the whole SE and not just “do it for looks” to keep time with others. I didn’t daven a good SE until I was in 6th grade or so after that incident. I would hate my good version of SE to be considered a sin if I blocked someone in by accident.