Use at your own risk...
This requires that you know the ID number of your custom profile field so go to the profile fields listing, hover the mouse over the button for editing and look at the number at the end of the URL:
So the above is 1, it will be used in the locations below where compared to $test
Edit core -> front -> global -> customFieldsDisplay
After:
{{foreach $fields as $field => $value}}
Add
{{$test = (int) str_replace('core_pfield_','',$field);}}
{{if $test != '1'}}
After:
</li>
Add:
{{endif}}
Edit forums > front -> topics -> postContainer
Before:
{{if $comment->author()->member_id}}
Add:
{{foreach $comment->author()->contentProfileFields() as $group => $fields}}
{{foreach $fields as $field => $value}}
{{$test = (int) str_replace('core_pfield_','',$field);}}
{{if $test == '1'}}
<li data-role='custom-field' class='ipsResponsive_hidePhone ipsType_break'>
{$value|raw}
</li>
{{endif}}
{{endforeach}}
{{endforeach}}
Result: