ECMAScript flavour, 30 bytes [cracked]
^((?![\t- ]|[^\s])(.)(?!\2))+$
Here is a rather simple one for the robbers to crack. It's conceptually not too hard, but might require a little research (or scripting). I don't intend to list myself in the leaderboard, but if someone cracks it within 72 hours, this will count towards their robber's score.
Tested on Regex101 and RegExr using Chrome.
Well, that was quick!
The regex was supposed to match any string consisting of distinct non-ASCII whitespace characters. However, I forgot a
.*before the\2, so it actually matches any string of non-ASCII whitespace, that doesn't contain two consecutive identical characters. There are 18 such characters in the Unicode range up to code point0xFFFF. The match posted by user23013 is one such string, consisting of 16 characters.