Try this:
<rules>
<rule name="bad referer" stopProcessing="true">
<match url="^(.*)" />
<conditions>
<add input="{HTTP_REFERER}" pattern="http://www.example.com(.*)" negate="true" />
</conditions>
<action type="Redirect" url="http://www.website.com/badreferer.aspx?bad=true" />
</rule>
</rules>
update:
<rule name="bad referer" stopProcessing="true">
<match url=".*" />
<conditions logicalGrouping="MatchAll" trackAllCaptures="true">
<add input="{REQUEST_URI}" pattern="/badreferer\.aspx?bad=true" negate="true" />
<add input="{HTTP_REFERER}" pattern="^www.\example\.com.*" />
</conditions>
<action type="Redirect" url="/badreferer.aspx?bad=true" appendQueryString="false" />
</rule>