OTHAR TRYGGVASSEN, Gentleman Adventurer! fits this, especially in the radio play, as lampshadedin this comic (of a radio play). Othar has been "kidnapped" by Ferretina, the Weasel Queen, famous for devouring young men, grilled with cheese. One of the closing questions is "And what kind of cheese goes best with grilled ham?"
Pushed even further into the zone of absolute hamminess by Cheyenne Wright portraying Othar in the audio plays.
Ferretina herself qualifies.
"I think it's the loneliness that makes a...person begin to have...strange thoughts. Thoughts that drive her to explore the twisted, blasphemous back alleys of science. That allows - no - forces her to create monstrosities! Monstrosities fit only to unleash upon those sanctimonious villagers who reviled and mocked her because of her father's experiments!"
Dr. Disaster from Gunnerkrigg Court. He starts hamming it up with his very first lines: "Spacemonauts! The Earth is in peril!" It's unclear whether he's like this all the time, or just acting. Ironically, he has a crush on Jones, the resident Stoic.
Parley knows how important it is to put up a good show (later, Mort joins too).
The Inexplicable Adventures of Bob! has Galatea ("CRAZY? YOU DARE?! ALL THE WORLD IS MAD AND ONLY I AM SANE!!") and Riboflavin ("I SAID BOW, YOU HALF-SENTIENT LEMUR!"). Galatea has a big crush on Riboflavin at one point.
Jake, despite his love for adventure and his tendency for Antiquated Linguistics, doesn't ham it up all that much until Aranea "heals" his mind so that he reaches his ultimate form, which regularly bellows Antiquated Linguistics in large, glowing, flaming letters.
Villains such as Caliborn and sober!Gamzee have their fair share of ham, too, and often to terrifying degree.
Dillon, the title character of Sticky Dilly Buns, appears to be a competent professional actor in-universe. However, he's prone to campness and flamboyant emoting, on and off stage, at least verging on ham.