Validating a Collection of IPv4s
The only simplification I can think of is using a bit more complex regex to match the IP address without having to iterate over the octets:

def valid?(proxies)
  return false if !proxies.is_a?(Array) || proxies.empty?
  ipv4_address = /^((25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d)\.){3}(25[0-5]|2[0-4]\d|1\d\d|[1-9]\d|\d):\d+$/
  proxies.each do |proxy|
    return false if proxy !~ ipv4_address
  end
  true
end


This regex is based on the one in the ipaddress package.