Acronym meaning: Laughing My Jizz Out
Alternative to the use of 'lmao' which means 'laughing my ass off'
Jizz refers to the male ejaculation of semen at sexual climax. Therefore to laugh ones 'jizz out' is to laugh so hard that semen is ejaculated.
Person 1: Look at that butterface!
Person 2: Lmjo!