Use $button->DESTROY to get rid of it.

The call to $mw->Button() returns a Button reference. You need that for the DESTROY call.

use Tk;
$mw = MainWindow->new;
for($i=0;$i<10;++$i) {
  my $b = $mw->Button(
    -relief => 'flat',
    -background =>"#FFFFFF",
    -width => 2,
    -height => 2,
    -text => "B $i",
  )->pack;
  $b->configure(-command => [ $b, 'DESTROY' ]);
}
MainLoop;
__END__
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The above code destroys a button when you click on it.