I've remarked on such meta-humor before, but they're usually isolated examples.
The first is from Bill Holbrook's On the Fastrack.
The first panel makes sense after you read the punchline. The word balloon is so common that -- as an object -- it's virtually invisible to the reader. Holbrook makes it a physical object in the first panel -- supported only by Deathany.
The next example was something of a surprise. I'm not a big fan of Mort Walker's Beetle Bailey. I find both the art and writing mundane.
In this case, though, there's some innovation. The characters know they're in a comic strip. If the second panel had stopped with Killer's comment, it would have been an adequate punchline. Zero's comment makes it better, as it builds on that. Killer points out that they can't read the strip that they're in. And Zero's comment goes a step further -- if they can't read the strip, then they certainly can't read the title above it.
The last example comes from Mike Lester's Mike du Jour.
The week-long running gag is that the office snack cart operator has been hosting cooking segments. Treating panel borders as physical objects isn't new, but it's used seldom enough to be refreshing.
And note that the hole Mike saws in the second panel is there in the third as well. All three panels show the same location at different times (in sequence, of course). If the panel borders were physical objects, then only the second one should have a hole. But since they're also boundaries of time, the third panel reproduces the damage of the second.
Not every paper runs Non Sequiter above Mike Du Jour. I wonder if creator Wiley Miller talked with Mike Lester. The panel is funny enough by itself. The victim standing on the X is reading about what will happen to him. Bystanders are all looking skyward, which is where the sign indicates "what you never saw coming" will be coming from.
But when you put the two strips together, then "what you never saw coming" actually seems to be coming up from below. So even the bystanders won't see "what you never saw coming."
I didn't see that coming when I opened up the paper May 10.