So far, nobody mentioned the absolutely worst one:
I Like My Monsters Rare. Enter game, check for spawns near your spot, kill if present, leave to the main menu, repeat - 10/10 IGN.
Other missions I really don’t like doing:
Death Race. Any tier is boring, tier 3 is just frustrating and pointless. I did it once to prove to myself I could do it, afterwards I did it multiplayer because I can’t be asked to bother with it. And while we are on the topic of missions that involve driving:
Arms Dealing. The timer is not that tight, I used to be able to do it easily, but it’s just so boring that I started to fail it. Since you actually have to fight enemies, I consider Customer Service and Neither Rain Not Sleet Not Skags to be fine. Not this one. Death Race might have been okay if you would actually kill bikers at times like the description says, instead you fail if you hit one.
All of Murderlins temple. The Magic Slaughter would be decent if the arena wasn’t what it is. The Magic of Childhood is just very uninteresting.
Then there are missions I can accept doing for the challenge they present, but still fail to be entertaining:
Twelve O’Clock High on UVHM difficuty. Flying enemies and high difficulty don’t mix well.
Bad Hair Day on non-melee characters.
Medical Mystery on UVHM before I realized a gun like the Blockhead works as well.
Get To Know Jack would be fine if you didn’t have to leave and re-enter the zone it starts in.