Could be a rude/annoying/unprofessional voice mail greeting, the way they answered the phone or refusal to talk to someone over the phone (text/email only demands), showing up with food and coffee, giving an off-putting attitude, speaking with a constant, purposeful vocal fry, etc.
Of course there are positions that don't require too much from employees, but what are some things that maybe acceptable under normal circumstances that you wish people would not do when they're job seeking and that may backfire on an applicant?