SWTLO Share definition Flag Short for sleeping with the lights on. Also seen in the form SWTLOed. This is the past tense form of SWTLO. Dude: I SWTLOed last night. Other Person: Did you see any monsters? Dude: Hell no SWTLO by The Wikipedian October 19, 2011 0 0 Get merch Get the SWTLO mug. Buy Now — $32.95 See more merch