The day Ma's ninja career ended

See it here.

The Dinette Set runs afoul of the English language trying to tell this joke, such as it is.

For starters, this trick is "for when you walk into a room and forget why." But, by the time you've walked into the room and forgotten, it's too late to start muttering to yourself. In fact, what is required is a total lifestyle change. You must constantly mutter your plans as you move, on the chance you might forget them (which would have the side effect of ruling out entire career paths, like street mugger, Navy SEAL, or Ninja assassin).

That said, if you have reached a point where the trade-off between how often you forget why you entered a room outweighs the annoyance of muttering to yourself, then you should probably seek medical advice from somewhere other than a gossip magazine.

Also, there's a slight misunderstanding regarding the meaning of the word "memory," apparently. If you walk from room to room muttering to yourself what your plans are, you are not really committing your plans to memory, you are insuring they never actually go into memory, but always remain in the forefront of your mind. So, technically, this is not a memory trick.

Even allowing for these obvious issues, the point of the panel is a bit obscure.

On one hand, it's possible this is commentary on the creeping senility of Joy's mother since she takes Joy up on the suggestion. Apparently she knows that, despite the physical and locational clues, she will be unable to remember why she walked into the bathroom once she arrives.

On the other hand, it's possible this is supposed to be commentary on how idiotic the initial suggestion is, by illustrating in the most scatalogical terms the effect of voicing one's intentions aloud. I admit this is the most plausible reading. But that would also make this a Straw Man joke. The memory trick is not a piece of common wisdom which is skewered for our amusement. It is an idiotic suggestion manufactured just for the occasion and ease of skewering it.

Then again, it's possible the panel is all an elaborate set-up to enable a reference Ma and the bathroom. The artist appears to find jokes involving Ma and the bathroom compelling, whereas the image makes me want to drink myself into a stupor (or at least until I resemble the crazy-eyed person in the Cialis ad).

I vaguely remember seeing these marginalia somewhere:

• Burl's spidey-sense is tingling.
  
• Is every wall of their house adorned with a clown picture? They seem to be a common element of The Dinette Set for the purposes of neutral commentary. Though in true Dinette Set fashion, the clown's range of expression is limited, in this case to wide-eyed surprise, which also limits the effectiveness of the commentary.
• Award points for creative spelling of the word "Vedge." I assume that is supposed to be "Veg" as in "Veg out."
• Speaking of which, the trio of marginalia regarding general laziness (two mugs, Burl's shirt) appear to be left over from a different panel, since they are unrelated to this one.