「それを乗り越えて、初めて少年は男にうんちゃらかんちゃらです」「何となくよさげな事を言おうってんなら、最後までちゃんと言えよ！」

「、」「、！」

'It's only by getting past that, that a boy first becomes a man... and blah blah blah.' 'If you're gonna say something that sounds vaguely profound, finish the sentence properly!'

Literal

''That [object-を] cross-over, first-time boy [topic-は] man [locative-に] blah-blah-blah is'' ''Somehow nice-seeming thing [object-を] say-want-[quotative-ってんなら], to-the-end properly say [imperative-えよ]!''

A comedic scene. うんちゃらかんちゃら is a nonsense placeholder filler similar to 'blah blah blah' or 'yadda yadda' — used when the speaker trails off or can't remember. よさげ is a colloquial combination of いい ('good') + ~げ ('seeming'), meaning 'seeming good, promising'. ってんなら is the casual contraction of と言うのなら ('if you mean to say'). 言えよ is the plain imperative of 言う + assertive よ.