Ok. Thanks again for all of your suggestions!!!
First, if the "wiseass"ness doesn't resolve soon, then I will be moving on. I don't think anyone deserves to be treated like that if they don't act like that themselves.
Also, on the flip side, after 4 years of being in a relationship with someone, I don't think it's a good idea to cut the cord without going through some kind of procedure that could very well lead to a resolution.
Second, there is a trend in his family for people to either 1) overreact by turning anything into a doom-and-gloom type of situation 2) attack others whenever the person feels like he/she is being criticized, whether it was intended to be critical or not or 3) to be antagonistic until the situation turns into a verbal slaughter that inadvertently harms the other person due to overstepping personal boundaries.
(This is just so fantastic, NOT! ...although I think it's fixable, at least in his case because he can be very reasonable and thoughtful.)
So thinkythinker42, I agree that temperament can flow through a person's family with or without it being intentional. The type of negative temperament that seems to have been taught within his family, which you can see in his mother sometimes, also seems to be hellbent on sticking around, too. Lovely!
Third, I am trying to be very straightforward and upfront with what I need to change. As Neurofizzy said, I can't waiver or my efforts will be ineffective.
After ignoring his antagonistic behavior last night and earlier today (which oddly resulted in a significant amount of guilt from my SO --> after I got off from work, I came back to a super clean apartment, a nicely wrapped present with a handmade bow, and groceries), I plan to separate myself, each and every time, from the snide and snarky comments until this gets resolved.
I think everyone who suggested this within the thread was right on target! (BB, Cassi, Ganymede, et al.) What doesn't kill me will make me stronger, right?
Sometimes I find myself caving to pressure whenever I shouldn't, so I will try my best to hold my ground and make it very clear that I do not want to be part of a wiseass's verbal target practice.