"In the IT world, regular expressions searches justifiably have gained a reputation for being fiendishly complicated. Instagram’s regular expressions for finding emojis may be the most complicated yet."

This stack overflow post [1] and Perl module [2] both come mind.

[0] http://stackoverflow.com/questions/1732348/regex-match-open-... [1] http://www.ex-parrot.com/pdw/Mail-RFC822-Address.html