LMAOSMK is the chat/text lingo for Laughing My Ass Off Slapping/Smacking My Knees. This is normally used when a simple LMAO just doesn't fit the occasion. LMAOSMK can be used on occasions that someone falls, someone tells a really good joke that you haven't heard before, it can also be used for those moments that you laugh until you can't breathe and the slapping/smacking of the knees actually reminds you to take a breath in before you pass the fuck out.

When you eat dirt for the first time and leave your family to build a shack in the woods