We're all on gradle and we had a new guy who started a project with Maven. He also used atom editor for Java/Scala code (even though we had a license for Intellij), and refused to use anything with code completion (or turned it off if there was an option). My boss had to explain basic git branching to him, his pull requests were missing build files, READMEs and he'd check in tons of scripts to run things instead of using maven/gradle.

I just thought he was weird, but I didn't look at his pull requests close enough to realize how bad his code was, until they fired him earlier this week.