Always good to find another Heinlein fan! I want to live in his future.
The online dictionary lists three definitions for "pixilated"
1. Behaving as if mentally unbalanced; very eccentric.
2. Whimsical; prankish.
3. Slang. Intoxicated; drunk.
Adobe Photoshop uses "pixilate" for a process that breaks photos up as if they are a fine, bright mosaic.
And I am not sure if it is an etymology or serendipitous, but the name certainly suggests that one who is "pixilated" is what we also refer to as "gang awa' wi' the fairies."