If this were CSI instead of CIDU, and the villain had covered something up with marker pen, we could just shine some ultraviolet or powerful visual-band light of the best narrow frequency, and see right off what’s under there.
But at this remove the best we can do is go by shapes. And by guessing whether Teresa would more likely josh one of her friends in the cartooning world, or genuinely insult someone whose tolerance she is willing to test.
Oh, wait, wait! Or are these layabouts in the coffee shop the real targets, and the comic they’re putting down is Frog Applause itself … in a different spelling?
Comics I Don't Understand 
It’s Pearls Before Swine isn’t it?
@Ian, that’s actually a pretty good guess. Pastis occasionally does crossover gags with other comics, and he’s not above making this sort of joke about his own work.
Ian has it @1: all of the ascenders and descenders poking out from the scribbling match perfectly with PBS. That said, I don’t think that Ms. Burritt was necessarily unloading on Mr. Pastis. The joke in this strip works equally well no matter which name is (illegibly) lettered into the first panel. She may have (rightfully) felt that it would carry more authenticity if actual letters were underneath the scribbling, and in choosing PBS, she has a target who is known to have a good sense of humor about such things. Other authors (of truly lame comic strips) might have reacted with a lawsuit.
I, the other Ian, agree with the first Ian that it’s Pearls before Swine. From both “what the words look like”, the broad description of the strip, and the way in which Pastis would likely, correctly, interpret this as a friendly ribbing rather than an actual attack.
I also just showed it to my wife, having opened it in another window without comments visible, to see what she would say without being influenced by other people’s guesses. After about five seconds of thinking, she said, “‘Pearls Before Swine’, maybe?” So, that’s five of us so far.
Make that six. It looks like Pearls to me, too, and they are known for their puns & often low-level humor. I don’t read it out of pity, though. It’s one of my favorite strips!
The proof is in the pudding . . . or in today’s strip . . .
Definitely Pearls Before Swine. It is a daily must-read/must-groan.
Nitpickery: Why does the guy answer with a specific strip, instead of just saying “the comic page”, “the funnies”, or some other description of the aggregate in his hand? It’s a bit like somebody asking “What are you eating?” and getting the answer “a little slice of cucumber” as opposed to “a salad”.
It would make sense if he was clearly stalled on the offending item, such as a particularly oblique “Far Side”. But he clearly understands the intended gag, even if it fails to amuse him, and even non-ironic pity is unlikely to keep him fixated on that one out of many.