Regular expressions are exact things.
You have:
(?#Jester's Cap) The Jester inspires ([\w\S]+)\.
It should be:
(?#Jester's Cap)The Jester inspires ([\w\S]+)\.
No space between the ')' and the 'T'.
Trigger condition should be 1 player or 0 seconds.
Keep in mind you have to be in range to see it. You can cap someone from beyond the range that you'll see the flavor text. Having the shadow AA has nothing to do with it. All versions of Jester's give that emote.
<edit>
To be more rigorous:
You can always test out to see if a regexp is working by right clicking on an encounter where you used it, bringing up the encounter log, plugging in the regexp, and searching as regexp. If it doesn't find anything, and a matching log line exists in the log, then your regexp is wrong. Most of the time it's a spacing or capitalization error. To remove the possibility of caps errors, you can throw in a (?i) to turn off case sensitivity, like:
Code:
(?#Jester's Cap)(?i)The Jester inspires ([\w\S]+)\.
And then it won't matter if you got a cap wrong somewhere.