TF2 weapons that seem incapable of damaging func_breakables:
I was at a threshold of 35 damage and strength 100. Ambassador still hadn't broken one after some 70 shots, whereupon it died to a single knife thrust (max 54 damage), so it appeared to be doing damage, it just couldn't finish the job. Arrows likely broke and fell away without dealing damage for the same reason that stickies can't attach to them (as the arrows like to pin themselves into things--likewise Needle Gun needles disappeared, though the damage was too low to test to see if they would also have an issue breaking the brush).
The OnTakeDamage output currently isn't fired at least in CS:S. I used OnHealthChanged instead. --MBit 07:17, 21 September 2011 (PDT)