A reader sent me an email asking me for information on the relationship between the Japanese trilled R, yakuza speech, and working class masculinity. I found some posts which I thought might be interesting for readers of this blog, as well:
First, this Stack Exchange post:
If you're referring to the kind of allophone on /r/ that typically appears in yakuza speech, as you said yourself, it is called 巻き舌 (まきじた) in Japanese. Phonetically speaking, it's the alveolar trill.
This is not one of the allophones the average native Japanese speaker would use when speaking in standard Japanese in normal context. As the Japanese Wikipedia article on the alveolar trill says, this allophone is most typically associated with the dialects(?) called べらんめえ調 spoken by 江戸っ子 (えどっこ) and 浜言葉 typically stereotyped as fishermen's speech, and a certain aggressive, hostile, and rough register in spoken language (such as typical yakuza speech).
And this one:
As you probably already read in the question on dialects, Yakuzas are often pictured speaking Hiroshima-ben on TV. According to Japanese friends, this has probably as much to do with the fact that Hiroshima-ben naturally sounds quite hard to the ear (whereas soft-spoken Kyoto-ben is the typical dialect choice for cute, feminine characters) as any real-world trend.
In reality, I'd say your average yakuza speaks a slang-heavy, ultra-masculine version of whatever his (or his clan's) native dialect is. As it happens, many yakuzas do come from Hiroshima and the West of Japan in general, so Kansai-ish accent is usually a safe bet (once again: Kansai-ben(s) tend to sound harsher and more direct than other dialects, so there's that too). Pretty sure the none-to-rare Osaka yakusa speaks exclusively osaka-ben...
As you already guessed, among obvious (possibly stereotypical) characteristics are:
1) extreme rolling of 'R's and ample exaggerated consonant gemination...
Addendum: talked some more with (Japanese) friends about this and the consensus was that there ultimately isn't any fundamental difference between "Yakusa-speech" and heavily-masculinised working-class osaka-ben (or hiroshima-ben, or whatever you pick).
Also found this humorous website that has some audio samples of yakuza speech in film. In the one titled 'stick out your finger', the trilled r is quite audible.
In short, someone wanting to learn more about this may want to investigate hiroshima-ben and its association with masculinity, working class identity, and yakuza. If you speak any Japanese, you could also try to search for '巻き舌 (まきじた)' on the Japanese net. I tried searching through JSTOR but didn't find anything on the alveolar trill in Japanese.