One thing here is that when you define an action on two things, you usually want to have the word “it” and a preposition, which tells Inform the syntax for how to refer to both things. For instance (this may not be the exact definition from the Standard Rules):
Inserting it into is an action applying to two things.
tells Inform that the action is going to be referred to in the source code as “Inserting foo into bar” or whatever. (This is just for the source code! Any commands for the action, like PUT LOTION IN BASKET, will have to be taken care of with “Understand” lines.)
So in your case you probably want something like:
Memeing it with is an action applying to two things.
Understand "use [something] on [something]" as memeing it with.
Carry out memeing something (called X) on something (called Y): [random coding stuff]
Also note that you can use “[something]” in the Understand line if you want to use a generic thing. If you define item1 and item2 as kinds and use “[item1]” and “[item2]” in your Understand lines, then the commands will only be understood for things that you’ve specifically defined as belonging to the item1/item2 kinds, respectively.