All of these are things my group has tried (some with more success than others)

* No, you may not HiPS by using the shadow created by your finger.

* The Female Paladin (with a 20 Cha) in a chainmail bikini's breasts are not allowed to be used for HiPS, either.

* The Giant's loincloth is right out.

* When playing the Cavalier class in Pathfinder, you are not allowed to do 45 (Power Attack) + 80 (Challenge) + 20 (Weapon Enhancement) + 45 (Strength) = 190 damage on the charge... and then ask if you really need to roll the 4d8, too.

* The Druid may not spend all his money on Wild Full Plate because he forgot Druids can't wear metal.

* Should the Druid waste his money in such a way, the GM shouldn't be a jerk and gloat about it.

* Should the GM gloat about it, the Druid is definitely not allowed to completely outclass the Fighter while naked.

* If the Fighter is completely outclassed by the naked Druid, the player should temporarily be allowed both the Throw Anything feat, as well as Catch Off Guard. Not the character, the player.