His face looks like a collection of balls stuck together, except for his beard, which comes off.
When he has a stomachache, it's quite clear that his abdomen is rectangular.
He offers Agrias an "animo" tape he was keeping in his shirt by letting it slide out (without moving, mind you), which for some reason is covered in mysterious purple goo. That makes her laptop BSOD.
He floats down slowly when falling, as though suspended by balloons.
Bizarre Alien Senses: M Dude can only see people as entities of pure light, which glow increasingly bright depending on how pathetic they are. Ronnie, of course, is one of the brightest people he's ever seen- literally.
Blessed with Suck: Ronnie's "magic fat". Any shirt that Ronnie puts on that is not a Hawaiian shirt turns into a Hawaiian shirt (except, apparently, the one in this very page's image). In fact, any object that makes contact with Ronnie's torso is turned into a Hawaiian shirt... without changing size. A fly that lands on Ronnie's torso turns into a tiny Hawaiian shirt, for example. Ronnie gets this from his dad, who has the same problem, but with Santa outfits instead of Hawaiian shirts.
Humanoid Abomination: "Runnie's replace", as it calls itself. A tall... thing with Bizarre Alien Biology, a face that appears to be made of balloons and talks in horribly mangled English. Sometimes it shows up when "Runnie is feel unwell" and does nothing except a weird mockery of Ronnie's daily behavior (except that one time it tried to kill itself) and creep the hell out of Agrias. Absolutely no explanation is ever given about what it is.
The Halloween 2014 comic provides an answer: he's a "replacement" unconsciously created by Ronnie.
Like Father, Like Son: Ronnie gets a lot of traits from his dad Santa. His rotund figure (and the "magic fat" that comes with it) and a "motivation creature" (Santa's is the Krampus) are the two big ones.
Limited Wardrobe: Ronnie's Hawaiian shirts, thanks to his "magic fat", as explained above.
Nervous Wreck: Ronnie is constantly paranoid about what other people think about him, going to great lengths to save himself from embarrassment (although this often backfires and Ronnie ends up humiliated anyway). He's also easily startled by loud noises and tends to get emotionally overwhelmed at extremely trivial shortcomings. Even thinking about something sad will reduce him to a cripplingly-depressed (and naked) puddle.
Not So Different: Agrias and Ronnie. They share the same love for comics and video games. And while Ronnie is far more socially awkward, Agrias can prove herself quite weird, if not disgusting, too. She gets to realize this in this strip.