It means lots of different things tbh. In motorbiking, traditionally it’s the officer worker who spends all week in a suit and all weekend in denim ‘n’ levvers, it’s pretty derogatory- basically an accusation of fakeness, people who want to put the lifestyle on for a day or two but not live it full time.
With the TA I guess it’s pretty literal, and since terrys I know use the term happily I guess there’s no insult.
According to the philosphers Bailey and Dickinson it’s people who get tanked up with their mates at the weekend and get in aggro then regret it on monday.
I don’t really know what it’s supposed to mean for mountain bikers tbh, just doesn’t really seem to make much sense. Lots of people only ride at the weekend, it’s a hobby not a scene/lifestyle.