$FORM{'comments'} =~ /\b$_\b/ }
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That may give errors or unexpected behaviour if there are metachars for REs in @blocked (e.g. opening parantheses, dots, ...). Either use quotemeta for each $_, or \Q$_\E, e.g.

@blocks = map { quotemeta($_) } @blocks;
... $FORM{'comments'} =~ /\b$_\b/
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$FORM{'comments'} =~ /\b\Q$_\E\b/
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