[RedTyger]

Easily done, if you're OK with modifying templates. In the threadbit template, you can use this to alter the appearance of the threadbit (each section dedicated to a thread in a list of threads).

<if condition=" $thread[voteavg] AND $thread[voteavg] < 2">
Your threadbit template for rubbish threads
<else />
The contents of your normal threadbit template
</if>

The 2 is the limit for the thread's average vote, so it'll kick in a 1.99 or less average. Just change the number to what you want.