Three or more hashtags.
#[^#]+#[^#]+#
Long hashtags (15+ characters): #hashtagpunchline
#[^ ]{15}
CamelCase hashtags (3+ Words): #NotSelfAware
#[^a-z ]+[^A-Z ]+[^a-z ]+[^A-Z ]+[^a-z ]+[^ ]*
Unforgivable word shortening: I'm near ur place r u busy?
\sur\s
\sr\s
\su\s
Mass conversations (4+ Mentions): @guy @dude @otherguy @man totally.
@[^@]+@[^@]+@[^@]+@
Retweet chains (2+ RTs): OMG RT @teengirlsquad RT @beebz I'm thinking of you.
RT[^RT]+RT
Mentions with only a URL (spam): @imathis tinyurl.com/spam
^@imathis *https?://[^ ]+$
Annoyingly extended words (4+ of the same letter in a phrase): OOOOHHHHMMMMYYYYGGGGOOOODDDD
([a-z])/1{4}
Tweet w/ just a single hashtag: #omgthissucks
^ *#[^ ]+$
Not a regex, but self retweets: In case you missed it I pooped this morning :)
In case you missed it
##App Location Updates
(updated for multiple words in Location name)
Path app location updates: (at Location) - path.com/foo
\(at [a-zA-z0-9_ ]*\) — http://[^ ]+$
Foursquare app location updates: w/ @twittername 4sq.com/foo
w/ @[^@]+ http://[^ ]+$
More Foursquare app location updates: w/ 8 others 4sq.com/foo
w/ [0-9]+ others http://[^ ]+$
Yet more Foursquare app location updates (seriously...): (@ Location w/ 4 others) 4sq.com/foo
\(@ [a-zA-Z0-9_/ ] w/ [0-9]+ others*\) http://[^ ]+$