Inflation
Explanation
This comic takes the economics concept of "adjusting for inflation" and applies it to a sexual context for comic effect.
A man in bed declares: "Okay, but adjusting for inflation, that lasted over 7.9 minutes!" He follows up with: "And I was HUGE!" His partner stares at him with a deadpan expression.
The caption reads: "Never have sex with an economist."
The joke works on two levels. In economics, "adjusting for inflation" means recalculating a value to account for the decreased purchasing power of currency over time -- making past figures comparable to present ones. The man is applying this concept to his sexual performance, implying that if you adjust the metrics using some favorable economic formula, his stamina and size were actually impressive.
Of course, this is nonsensical -- physical duration and size don't inflate or deflate like currency. The humor comes from the absurdity of someone so steeped in economic thinking that they can't help but reframe embarrassing personal realities through economic jargon. The partner's unimpressed expression and the caption's deadpan advice ("never have sex with an economist") seal the joke: no amount of creative statistical adjustment can salvage the situation.