I'm collaborating on a scientific writing project with three other authors. Writing has been pretty rocky so far because one of the major collaborators is an objectively terrible writer.
Sections they've written that are meant to be highly technical are written as a meandering stream of consciousness full of incomplete sentences and off-putting juxtapositions of unnecessary jargon with an informal conversational tone:
Example: "A spectrally Φ-reweighted helix-referenced free energy perturbation summation, so to speak."
They have made "revisions" to parts I've written that introduced grammatical errors, misused words, and run-on sentences.
Unfortunately, due to the circumstances of the project, this collaborator is the first author of the work. The rest of us have too much professional decorum for our own good and haven't told them how much their writing sucks.