environment.rb

ActiveSupport::CoreExtensions::Time::Conversions::DATE_FORMATS.merge!(
  :simple => "%I:%M %p %Z, %Y-%m-%d",
  :month_year  => '%b %Y',
  :month       => '%B',
  :year        => '%Y',
  :day_of_week => '%a',
  :day         => '%Y-%b-%d',
  :date        => '%Y-%b-%d',
  :default     => '%b %d, %Y at %I:%M %p %Z',
  :datetime    => '%Y-%m-%d at %I:%M %p %Z',
  :time        => '%I:%M%P %Z',
  :us          => '%b %d, %Y',
  :us_no_year  => '%b %d',
  :date_time12 => "%m/%d/%Y %I:%M%p",
  :date_time24 => "%m/%d/%Y %H:%M",
  :iso_8601_date_only => "%Y-%m-%d",
  :iso_8601_time_only => "%H:%M:%S%z"
)

some_view.html.haml

= Time.now.to_s(:simple)