The clip comes from the long running party van joke tied to 4chan's video game board and the Team Fortress 2 community, where group in jokes and voice spam were a big part of early online gaming humour. Sounds from those circles spread through forums, game servers and soundboards because they were short, loud and easy to recognise out of context. This lmao clip survives for the same reason, working as a shared reaction that older gaming audiences instantly read as everyone laughing together at something stupid.