Laddism is the name people gave to that whole British style: young men drinking a lot, caring mainly about sport, sex, and music, and treating seriousness as a bit of a joke. Magazines, certain comedians, certain football culture. Writers used laddism when they wanted the attitude as a thing, not just one person. Some wore it lightly. Some blamed it for rude or sexist behaviour. You will mostly meet it in writing about Britain from the 1990s on. It is not a school word, and American English barely uses it.