Well, all things considered, either Kaidan or Ashley in ME2 specifically.
It's like...
Shepard: " Oh hey! S'been a while huh? "
K / A: " Sh- Shepard? Wow it's really you! What happened to you?! "
Shepard: " Oh I got killed during that attack on the Normandy. My body was found, then I got resurrected by some crazy procedure, took about two years... Liara has more details though. But now I'm back and kickin' some serious arse. "
K / A: " Well th- that's... amazing! So hummm... I was sort of sent here in part because I had to check to see if Cerberus was behind those abductions on our colonies, do you know anything about that? "
Shepard: " Well yeah I know it's not Cerberus now, 'coz I'm with them now to check if ther- "
K / A: " You're with Cerberus ?! "
Shepard: " ...well, working "with" them yeah, didn't have much choice apparently. "
K / A: " What the hell Shepard! "
Shepard: " Whut? Look, some guy forced me into this position, I didn't actually ask for it, you realize that much, right? "
K / A: " What are you talking about ? "
Shepard: " Some guy wrote me into this position and the people controlling me had no choice but to follow suit with this crap, so now I'm "with" Cerberus... s'not like I can't also use this opportunity to destroy them from inside while I'm at it, right? You know me anyway, hey we've stopped a Reaper two years ago and saved the galaxy, remember? "
K / A: " Ok, look, I don't understand what you're talking about, and I don't care to. Yeah ok we saved the galaxy and I and countless others owe our lives to you, so what? Now you're a monster and I feel like I want to cry out all the water contained in my body. I should just arrest you right now! "
Shepard: " Are you kidding me? What the **** are you on exactly? I'm Shepard!!! I'm not here to start a galactic-wide empire! Well... ok the Illusive Man might do that at some point but I won't be part of it. I'll come back with the Alliance once I get to the bottom of all this Collectors crap, and I'm gonna use Cerberus resources to do whatever needs to be done right now to save humans and our colonies. "
K / A: " I don't know who you are anymore... I'll... just go... * slowly shakes head in disbelief *
Shepard: " Ok, you know what? F-You., and next time I'm gonna have to save this **** hole of a galaxy I'll remember to count you out of the party. I'll remember this, believe me. "
And I sure did remember, ignored them as much as I possibly could in ME3 (well, Kaidan in my case).