Hmm. I just did a quick check -- This may well be true, though whether or not Slob knows this through experience or through the same method as I do I don't know. Myself, I opened the script files. The material default configuration gives all materials the variable InteractionFlags = CAN_DISSOLVE. Some materials (mithril, for example) have a line (InteractionFlags = &~CAN_DISSOLVE) which I'm assuming removes this flag. Give me a moment and I'll compile a full list of materials immune to acid:
Valpurium
Mithril
Gold
Diamond
Silver
Sapphire
Ruby
Golden Eagle Feather
Dragon Hide
Arcanite
Illithium
Octiron
all Light Crystals
Frog, Elpuri, and Daemon Flesh
Actually with enough leg strength you don't need boots. My winner was able to kick down the balsa walls in UT1. If you want something more impressive poly into a, say, mithril golem and try kicking down just about anything. Or just change your legs into that material.
Throwing on the other hand... yeah, that ought to be able to break down at least room walls.
Also Neon, you forgot the couches dropped by Eddies, and I believe there are also beds here and there (in the cathedral perhaps? I seem to recall seeing/hearing about them...)