in Henry's book he talks about a young actor who joined the show in the later seasons who developed a big ego. he was getting popular and would bring his fan mail to the set and sort of brag about it to the other actors. henry took him aside and politely told him he shouldn't do that. the actor said okay but kept doing it. The actor was written out of the show not long after. who is he talking about? the only young actors i could think of were Flip or Melvin Belvin.

I almost want to believe that Henry Winkler could be talking about Scott Baio (Chachi (https://happydays.fandom.com/wiki/Chachi_Arcola)). He did join the show in the fifth season, so he wasn't always there. Then again, I don't know if Season 5 could be defined as being one of Happy Days' "later seasons" (which could be defined as the ones without Ron Howard and Donny Most) if it was on the air for six more seasons after that.

And Scott Baio was ultimately written out of Happy Days but that was for the ill-fated Joanie Loves Chachi spin-off (which was concurrent with Season 10 (https://en.wikipedia.org/wiki/Happy_Days_season_10) of Happy Days) before being shipped back to Happy Days along with Erin Moran.