A second example of this phenomenon is culled from my best friends. While they're arguing, they'll say "I concede your point." This isn't a type of spelling error (as in the first example) because they say it all out loud, but I don't think it's a spelling issue anyway . . .
Now, in the first example, the guy meant "might as well." My girlfriend and I had a heckuva time thinking of what he meant. In the second example, while "concede" works here, I think they're bastardizing "can see, and it drives me nutso every time I hear them say it.
Is this an example of what happens where people misunderstand lyrics and their brain fills in the words (the term escapes me at the moment), or another phenomenon entirely?