Well, strictly speaking, it was sarcasm in the form of a suggestion:
There’s a collection of why- and how-interrogative forms that, in addition to their literal question-asking meanings, can be conventionally used to make suggestions, and suggestions can be uttered sarcastically to reverse their polarity, as in the following set:
Why don’t you like me? [literal information question]
Why don’t you have dinner with me? [suggestion, for joint dining]
Why don’t you just jump off the fuckin’ roof, you moron?! [sarcasm, conveying that it would be stupid of you to jump off the roof (or to do something relevantly like jumping off the roof), hence suggesting (strongly) that you shouldn't do that]
I’ve overloaded the last example with features (including the orthographic device ?! to indicate the very high rising-falling final intonation of an emphatic interrogative that might be intended to convey sarcasm) that point to sarcasm, but in actual life things are very often not so dramatically underlined by linguistic features.
Faced with utterances that could be unclear as to the speaker’s intent, the hearer might just fail to get the sarcasm and interpret an utterance like Jeremy’s as a suggestion. Or, more deviously, the hearer can reject the intent behind the speaker’s sarcasm and affect not to get the sarcasm, by treating the utterance as a simple suggestion. We can’t be sure which route Jeremy’s mother has taken, so the strip might be “about” the cluelessness of parents or “about” their resistance to their kids’ (unreasonable) opinions in opposition to their (of course, entirely reasonable) requirements. Or both.
