Executive Meddling: Cherry's introduction in the manga series. Roman remarks it was a request from the editor to let there be some fanservice in the series (something that Shinohara often avoided). And oh boy, the main cast know that something is going to go wrong when he appears in it.
First Appearance: With the difference of exclusive characters in both one-shots, and the appearance of the Sket Dan (with minor design differences), Otakura and Yabasawa made their debuts in the first Akamaru Jump one shot, and the rest, they say, it's history.
Some JoJo's Bizarre Adventure one: Kazuyuki Okitsu, Jonathan Joestar, did a minor role in the anime and he has a talk of sorts with Switch. Sugita voiced Joseph Joestar, his grandson in the TV animation series (and the All Star Battle videogame), and is a great fan of Jojo in real life as well (hence his references of the 'WRYYYY' scream in the series could be his inner fanboy as well).
Talking to Himself: Happened plenty in the Sket Dance/Gintama crossovers, especially with Gintoki and Switch. And with Teppei and Shinpachi.
Technically, Bossun's dad never interacted with his son, but his letter made it look like so in the 'Happy Birthday' episodes, and since Hiroyuki Yoshino was both voices (being a bit of a mythology gag from the manga), it could count as talking to himself.