You see, despite the fact that leather jackets are now reserved for people on the rear end of a mid-life crisis,when Happy Days was first conceived they were seen as the fashion choice of a no good ruffian. However, the shows creators, really, really wanted Fonzie to wear a leather Jacket, because nothing is more sweet and bitchin than tight leather. However, the studio executives stood steadfast on their decision that Fonzie couldn’t wear the item of clothing that would eventually come to define his character.
Which is when the creators had a genius idea, they quickly realised that leather jackets were considered a necessary safety requirement for bike riding and that if Fonzie was on a bike, he’d have to wear a leather jacket, otherwise he’d be setting a bad example. So, they simply made every scene involving Fonzie involve him and his bike, even if it made no sense for it to be there, like when he was in a diner. That way, the studio executives could do nothing but watch Henry Winkler sit, in a leather jacket, polluting the minds of young children with his infinite coolness on a bike that steadily started to resemble a giant metal, middle finger. Sit on it!