I am sure this has happened to all of us in some extent with some variations.

Colleague not writing comments on code.
Ask him something like "How am I suppose understand that piece of garbage you have written when there is no comments or documentation?"
This keeps happening for a long time. Some time after, I write a kernel module using idiomatic C and ASM blocks for optimizations (for some RTOS) and purposely not write neither documentation nor comments.
When he asked for an explanation, I answered to everything he questioned as general as I could for "that trivial piece of code".
After that he always documents his code!
Win! 🏆