[0]: imagine your colleague wrote a macro that redefines for loops because at the time, it made life easier for him.
This is like asking "what if your coworker named all errs as `ok`" so everything was `if ok { return errors.New("Not ok!!"); }`. It's possible but no one does it.
This is why `defmacro` and `gensym` in common lisp are awesome, and similarly why Go's warts don't matter. Much of programming language ugliness is an "impact x frequency" calculation, rather than one or the other.
It's also why javascript is so terrible, you run into it's warts constantly all day long.
But apparently lots of other people do run into them regularly, so I believe that such things do exist.
By the same token, I've heard countless reports of people struggling with the flexibility that Lisp offers, with co-workers who abuse it to create nightmarish situations. That you haven't experienced that doesn't mean no one does.
I don't mean "do dumb stuff", I mean I've literally never seen anyone redefine the `define` keyword in any code.
With javascript, I do see people use `===` frequently. It's a wart of the language that the operator even exist. It's not "dumb" to use it - it's how frequently are you assaulted with the bugs of the language (not bugs in your code).
You wouldn't let a child handle a chainsaw.
But I don't recall seeing someone re-define `define` in real life.
Nor do I recall seeing any problematic redefinitions in Scheme in real life.
That said, if you wanted to make a language variant in which `define` did something different than normal (say, for instrumentation, or for different semantics for variable syntax), then you'd probably use Racket, and you'd probably define your own `#lang`, so that the first line of files using your language would be something like `#lang myfunkylang`.
You can randomly sample code in <https://pkgs.racket-lang.org/>, and look for people doing anything other than `#lang racket/base` or `#lang typed/racket/base`.