test.rb

a = [{ :one => 1, :two => 2 }, { :one => 1, :two => 2 }, { :one => 2, :two => 1 }, { :one => 3, :two => 2 }]

def uniq(ary)
  b = []
  c = ary.dup

  while c.length > 1 do
    d = c.pop
    found = false
    c.each do |e|
      found ||= d === e
    end
    b.push(d) unless found
  end

  b.push(c[0])
end

p uniq(a)