Hmmm, confessions, eh?
I agree with the OP about Marauders and the sounds they make. Anyone who's played with me for any length of time has no doubt heard me impersonate them with a little "shooby dooby doo" after taking one out. LOL
I can't stop checking the scoreboard between waves. It's a terrible habit. I sometimes feel guilty while doing it. I TRY to actively remind myself not to when recording game footage because it makes me look like the hopeless score w***e I am. But there it is. I don't look down on anyone else for their own scores or mock anyone for them. I just like to see myself on top if I'm having a good game. I'm a terribly competitive Aries in that way.
I almost never cancel my Phoenix Adept's Smash animation. I know I should. It's a long animation and canceling it will help you not die so quickly, but I just love watching the full show.
I have totally paired up some of my MP characters together in my head. It's hilarious. It hasn't gone so far as to inspire fanfiction (yet), but it's there. In my head. Making me occasionally chuckle at inappropriate times in-game.
I do not enjoy playing the Asari kits. Any of them. Not even the Justicar, which would arguably be my "favorite" if I had to choose one. I have no earthly idea why. They're quick. They have a great evade. I love biotic explosions (especially the sound). And I can do fairly well with most of them. But I just can't get into them in a role-playing sense. At all. I literally feel like I'm just routinely going through the motions whenever I play one. It's sort of sad, really.
I kind of want a Vorcha for a pet. Their little sayings are adorable and my heart breaks every time I hear one in pain or bleeding out ("I'm DYING!"). Sounds so scared. As a result, I tend to be a little protective of them in-game, the way some people are about a Volus teammate. LOL
I love watching the Salarian's little side-stepping hop-dodge. I know it's the same animation as the Quarians and Geth, but for some reason the Salarians look the goofiest doing it.
I think the Drell's trenchcoat looks ridiculous. Sacrilege, I know, but that's how I feel. This isn't The Matrix, DrellGod. Put some freaking armor on, even just something light. And grab some for the Vorcha, too, while you're at it. Cripes. LOL
I could listen to the Male Quarian all day long. Read me the phone book, I don't care. Just don't stop talking to me.

I don't think the Batarians are that ugly.
Wiggly Krogan tails are the cutest thing in this game.