Printing taxonomy in title tag?

If a user clicks on a tag, I want to print the tag name in the title of the categories page. This doesn't seem to work:

<title>
        {{ _site_name }} 
        {{ if segment_1 }} – {{ title }} 
        {{elseif segment_2 == "tags" or segment_2 == "categories"}} – {{ taxonomy_slug|ucfirst }}
        {{ endif }}
    </title>

Any suggestions?