I know how it works but since RESDs special ability allows it to discard an equpped monster to negate the effect of a card targeting my monster, the same rule should go for Order to charge in that case.
You can negate an Order to Charge that targets a monster you control. The problem with that is that only the monster that's to be Tributed is targeted. (You select the monster to destroy when Order to Charge resolves.) So you're only ever going to be able to negate your OWN Order to Charge with Slash Dragon.
Quick thought tho, does the same rule apply to Tribute to the doomed? Cuz you discard a card from your hand in order to destroy a monster to the field, meaning it would be considered tributing a monster to destroy another monster. Would RESD be able to negate that?