I can understand the first half of the sentence just fine, but what does the character mean when he refers to his friends as "ノッて来ん"? Is it some form of slang or colloquial speech?
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It is a colloquial version of のってくる, where のる means to accept invitation, join (def #5 大辞泉 or def #7 プログレッシブ和英中辞典) and る is changed to ん. It means the speaker asks around for going out, and it is only guy-friends who are willing to join (ノッて来んの). Note that は is omitted and the part is a cleft sentence: ノッて来んのは男のダチばっかりだ. (Edited according to naruto's comment. This may also be relevant for what this の is, but practically you shouldn't worry too much.)
To me, the mix of katakana/kanji is slightly odd. のる is often written in katakana in the sense that the subject gets higher 'momentum' (in abstract sense, See def #10 in the 大辞泉), which to some extent overlaps in the sense being used.