The story
Per The Times of Israel: Saleh al-Jafarawi “gained wide attention with a video he recorded on October 7, 2023, in which he praised Hamas’s attack. Later in the war, he filmed himself crying in reaction to Israel’s airstrikes. Pro-Israel activists juxtaposed the two videos and gave him the nickname ‘Mr. FAFO’ (an acronym for ‘fuck around and find out.’)”.
Etymology from Wiktionary, CC BY-SA 4.0.