You could keep all these files together like the dumbing down series and even say all the personalities in the description up top, but not which personality goes with which color.
These are just suggestions you could use or you could come up with your own personalities. One could be a know-it-all file, with the user proving just how intelligent he/she is by using the most complicated words he/she can think of when simple words would do. One could be a trash-talker file, with the user using at least 2 obscenities each sentence.
One could be a slut file, with the user posting how horny he/she is. Have each file suggest that the person comment with a different personality. Label them with something innocuous like colors. Instead of having 1 file, have five files. Here is a suggestion on how to make it so both you and the user know it is really the post-hypnotic suggestion and not just the person acting out what he/she thinks the file is suppose to do. However, reading those comments was very entertaining, especially when I joined the ranks. The one thing that detracts a bit from the experience is that I(haha, he can say that again now) knew what was coming and expected of me before I even listened to the file because of all the comments.
