(If you’re puzzled by the odd symbols in the cartoon — Dan Piraro says there are 2 in this strip — see this Page.)
First, the adverb bad in I want you so bad. Then some notes on correction as a social practice, especially in one-on-one interactions.
Adverbs bad, badly. MWDEU has an entry (starting on p. 159) for these adverbs. On p. 160, it declares that
Bad is … interchangeable with badly after want or need
and go on to look at the history, which suggests that for some time bad was the prescrbed alternant. Indeed:
Viztelly 1906 and McCracken & Sanders 1917 (and many others of that era) warned aganst using badly after want in the sense of “very much”.
That is, in this context bad was the standard and badly a hypercorrection — presumably produced in the belief that adverbs should have the suffix -ly as a mark of their categorial status, and in reaction to the long-established and widespread, but definitely non-standard, use of bad, and other suffixless forms, as adverbs in other contexts, as in He was beaten up real bad (with a suffixless degree adverbial real and a suffixless extent adverbial bad).
But the hypercorrection spread among usage advisers (and probably misguided schoolteachers as well), until:
By 1958 [New York Times editor and Columbia University professor Theodore M.] Bernstein was correcting bad after want to badly, indicating that it was fully acceptable in this use… As we have seen, bad is frequent in this use, but most of our evidence is from speech.
Vernacular speech and informal writing, however, has stuck resolutely to bad with want and need, as is evidenced in this usage in pop music, where (as far as I can tell) badly never appears in this context. A small sampling of the relevant music, running from 1957 through 2015 (I especially recommend the first three:
1 B. B. King, “I Need You So Bad”, a 1957 blues single (you can listen to it here)
2 James Brown, “I Want You So Bad”, a 1959 soul single (you can listen to it here)
3 The Beatles, “I Want You (She’s So Heavy)”, rock from Abbey Road (1969), with the lines I want you, / I want you so bad, / It’s driving me mad (you can listen to an outtake here)
4 From Wikipedia: “I Want You So Bad” is a song recorded by American rock band Heart. It was composed by Tom Kelly and Billy Steinberg, who were responsible for writing Heart’s U.S. number-one single “Alone”. The track is a ballad sung by Ann Wilson, and it was released in a remixed form as the fourth and final single from Heart’s ninth studio album, Bad Animals , as well as being the band’s final single of the 1980s. [you can listen to it here]
5 The Vaccines, “I Want You So Bad”, from the 2015 album English Graffiti (you can listen to it here)
This is the context for the guy’s fervid assertion of desire in the top panel of the Bizarro cartoon. With adverb bad, entirely in line with informal standard English, and surely not any sort of inadvertent error on his part.
Digression. MWDEU also has a section on the adverb badly after copular be or a linking verb (especially the linking verb feel, as in I feel badly), a context in which a predicate adjective (like bad) is called for, and badly arises from hypercorrection. For extended discussion of this case, see two postings on Language Log by Mark Liberman:
from 4/23/09, “Prescribing terribly”
from 8/20/11, “Feeling bad(ly)”
Correction as a social practice. I reiterate: want you so bad is surely not any sort of inadvertent error on the guy’s part — call him Boner — and unless the object of his desire — call her Peeva — is totally deaf to the English used around her, she understands that. Yet Peeva corrects him. Why?
If we could quiz Peeva, no doubt she would say that she’s doing it for Boner’s own good, that she’s instructing him, in her smugly superior way, that in her opinion he should have used badly instead of bad. He’s pouring out his desperate desire for her, and she’s carping about his grammar, offering advice that wasn’t asked for and shifting the subject of their conversation away from the urgent matter at hand; even worse, her peevish complaint is deeply misguided.
But even if Boner has inadvertently said something he didn’t mean to, like I want you so bad it burts or I hurt you so bad it wants, so long as his intentions are clear, it’s at the very least impolite of Peeva to point this out, rather than just letting it pass or letting Boner correct himself. But it’s much worse than that. It’s like following his fervent declaration by complaining that the color of his shirt is unflattering to him, or that his hair needs cutting — an irrelevant personal criticism that derails Boner, who surely loses his, along with any interest he has in pursuing Peeva. (In my opinion, he’s well out of it.)
The larger point is that correction is always disruptive, so that it shouldn’t be undertaken without good reason.
Footnote: It was correction killed the desire. This title is an allusion to a crucial line from the 1933 movie King Kong: “Oh, no, it wasn’t the airplanes. It was Beauty killed the Beast.”