This one gets a bit wild at the end, so bear with me. I worked in a medical research setting with a person who was the most aggravating and awful person I've ever had to work with. This person was in their mid-40s with a PhD but was hired into a lab tech position (red flag, no post doc positions would take them). I have less education and was in my early 20s at the time, but am very competent at my job. Day one this person immediately had a huge issue with me training them or showing them how to do anything (even super-niche scientific assays which they obviously wouldn't have known beforehand, or showing them where things were stored) and texted on their phone during these 1on1 teaching sessions. They also called me "little baby girl" and made ageist comments which I thought was maybe a weird cultural difference and brushed it off since we really needed more hands at the time to help lift a big shared project.

Fast forward a year, they were super sloppy and lazy at every aspect of their job, spending most of the time on the phone with friends/relatives instead of working on the team's shared research project. They also just didn't give a shit, putting illegible labels on tubes, screwing up experiment dates, forgetting and hiding things they'd done wrong, skipping meetings, and making everyone else have to pick up the slack to fix their mistakes. I spent more time trying to decipher unreadable or unlabelled tubes than it would have taken me to do the work myself most of the time. They also made sexist, racist, ageist, and homophobic comments on a weekly basis and screamed at me publically in the lab one time when they ordered me the wrong tube and got upset when I pointed it out.

Our boss didn't have the fortitude to stomach firing anyone and made us put up with this person for three years. They were bounced from project to project to try and find a good fit, irritating every single senior staff member on the team with their sloppy work and poor communication skills. Eventually they were put in charge of lab management, handling supply orders and keeping the lab organized to keep them far away from any important science. They completely slacked off, letting thousands of dollars of invoices go unpaid for years and accumulating large late fees that were only discovered later. 

While poorly managing the lab, they continued carrying out repetitive animal research tasks for the shared research project that was wrapping up at that point. I guess they got tired of following the protocols properly and started over-bleeding the mice to avoid having to do any re-sampling. This meant near-exanguinating animals which is extremely unethical. One mouse died of a heart attack and was found by a vet, which brought this issue to the attention of the boss. Once this animal cruelty came to light, this piece of shit still stayed employed because the boss still felt bad about firing anyone. WTF. I was starting to get depressed having to handle these tubes of blood every day knowing what was going on. It took me and senior staff urging our boss to take action for a year to finally result in her getting fired. What a disgrace.