[parenthephobia]

    @sentence = @sentence.split(' ').map!{|x| x = x[0..0].upcase << x[1..-1]}.join(' ')

Nobody sensible would write this code. The nearest sane version is:

    @sentence = @sentence.split(' ').map{|x| x[0].upcase + x[1..-1]}.join(' ')

But, although capitalize doesn't do the same thing, it's almost certainly what is actually wanted, so it would be

    @sentence = @sentence.split(' ').map(&:capitalize).join(' ')

Having said that, it's much more likely that a "clever one-liner" would be

    @sentence.gsub!(/\b\w/){|x|x.upcase}

Code like the article's would generally not be the result of cleverness, but of code that has organically mutated into something silly you'd never have written from scratch that way.

[brobinson]

Huh, I've been doing Ruby since 2008 and I've never seen a block passed to gsub/gsub!. Neat!

That said, a block isn't necessary here and the one-liner can be even shorter:

    @sentence.gsub!(/\b\w/, &:upcase)

&: call syntax is actually a little faster post 1.9, too.