The worst was the CEO of a small competitor company repeatedly hassling me over slack DMs and in github issues threads shamelessly trying to get me to prioritize free work that he wanted for his clients. Separately, over a period of several weeks, this same person asked me a ton of support questions and then compiled my answers without edits or attribution into a "white paper" he used as a resource to get people into the marketing funnel for his consulting shop. I came to hate that guy, such an asshole, but I couldn't totally block him because his company was a member of the open source foundation governing the ecosystem of tools my project was under.
Honestly, it was hell. The most stress and irritation I've ever had in any job. When I started the job I thought it was a dream getting paid to do open source, but now I consider that an anti-goal for any future role.