sub rand_element (\@);

@array = ([1,2], [3,4], [5,6]);  # etc...
($k,$v) = rand_element(@array);

sub rand_element (\@) {
  my $aref = shift;
  my $idx = rand @$aref;
  my ($k,$v) = @{ $aref->[$idx] };
  my $last = pop @$aref;
  $aref->[$idx] = $last if $idx < @$aref;
  return ($k,$v);
}