The 'I Wonder What He's Thinking' meme, also known as 'He's Probably Thinking About Other Girls,' features a woman lying awake in bed looking suspicious while her partner lies beside her. The humor stems from the contrast between her internal fear that he is cheating or thinking of someone else, and the reality that he is actually contemplating something absurdly trivial, like video game lore, historical facts, or shower thoughts. It first gained massive popularity on platforms like Twitter and Reddit in late 2016, evolving into a versatile format for showcasing niche interests and relatable relationship dynamics.