Blue
Ravenous Bugblatter Beast of Traal
"Can I hit that guy hard enough that his breastplate comes loose and he doesn't benefit from that for his AC for the rest of the fight?"
(Most DMs say no way)
In a game like 4e, you just declare "I am using my Daily Power Crack the Shell," and roleplay out the attack and consequences.
Rule 0 still applies, but this time it's, as [MENTION=42582]pemerton[/MENTION] points out, earlier in the process (when the PC levels up and takes the power) rather than at the moment of using the power in order to maintain control of the narrative.
Umm, there's no need to ask the DM that, because he doesn't have a power int he first place to allow him to do it.
If the question really is "can I get super extra powers just by asking the DM", that's a whole different take than that he wants his powers to be reliable and not require "whim" like he's said several time.