The habitual jokester is a guy who read some jokes on a Reddit subforum and somehow developed a didactic memory for just the worst ones. He'll rattle them off one after another, and you can actually graph the decay of polite laughter into dread guffaws and finally hate chuckles as he goes. And just to be clear, this guy isn't necessarily telling knock-knock jokes, he may also dig deep in his soiled trick bag to pull out things like Borat impressions or oral re-tellings of memes.
Your only true defense against this terrible person is a Dirty Girl Scout. That's one shot creme de menthe and one shot Irish cream. Mixed together, it tastes like Bacchus himself threw up in your face after eating some Thin Mints and if you have about eight of them, this guy could tell you jokes about Trump's cabinet running a train on your mom and you'd still laugh.