I'm serious, I really don't get what this is about. That the research they've been doing isn't fun? But why would this one scientist say this? Doesn't make much sense and I clearly don't get the joke. Maybe someone can explain?
Researchers are specialists in their fields and have carved out an academic niche. They study a single thing for years at a time before publishing a paper, and the process of studying anything is brutally methodical and likely quite often boring until you maybe discover something. It's then boring again as you write your paper on your work, regardless of whether it discovered something or not.
All of a sudden, your co-researcher just turns to you and goes "Fuck it. Let's research something else tonight. Something fun as a treat".