Even so it's still likely to type the wrong url/login on the wrong device(i.e by reflex). The only safe choice you have is to not have any "personal stuff"(i.e. personal twitter account).

Possible, I know that a couple times a year but I would think a professional in that situation would use a completely different service for personal use. (I.e. Personal Twitter, Professional Reddit)

Well if the job requires you to use all of them(twitter, facebook, reddit) you are left with no service for personal use only.

Usually you don't have a choice, you use what your friends use.

The solution to that is to use a password manager, and save all your (randomly generated, long and unmemorizable) professional passwords only on the device that cannot connect into the open internet.