Updated post:
Compounds plural or compound plurals? That is the question …
We were already compiling a few notes about the “art of pluralizing” when we got a rash of input (from TV, Twitter, and email) about the plurals of compound nouns, specifically those compound nouns consisting of a noun plus a modifier.
We’re taking our best shots here, so please feel free to disagree or otherwise comment.
In question:
daddy longlegs – conventional wisdom would lead us to the plural form of: daddies longlegs, however, since that is cumbersome, we suggest: Harvestmen
Attorney General – no question about this one: Attorneys General
gin and tonic – conventional wisdom (gins and tonic) again loses out here (we defer to ironic1.com for this one ): gin and tonics
notary public – not much question with this one: notaries public
brother-in-law – consistent formation found for this plural: brothers-in-law
maid of honor – 1) for more than one honor: maid of honors; 2) for more than one wedding attendant: maids of honor (please, only one MOH per wedding); for more than one copy of the movie Made of Honor: we suggest DVDs.
man-of-war – encounter one and there are likely more on the beach or in the water: men-of-war
Bride of Chucky – ok, so are you talking about the plural of Chucky’s mates or the number of movies … or, even, the possessive? For our purposes here, today: Brides of Chucky
Good, now we’re getting more input. In a recent Twitter conversation:
@NeillShenton to @GrammarCops “ok, what about multiple spoons full of something? Plural* me that – i’d rather rephrase a sentence than type THAT ugly word.”
* We’re now adding “plural” to our list of Nouns gone bad … Thanks!
@GrammarCops to @NeillShenton “Good one … it’s actually one word ‘spoonfuls.'”
There are likely hundreds of such examples. Please contribute.
Grammar Police a.k.a. GrammarCops 
I would always go with Gins and tonic- you’re ordering two separate drinks (the gins) and a tonic to go in both of them.
Enjoy to your heart’s content! We’ll just go for the margaritas :-).
We’ve run into this difficulty while writing a test for students to take. I am of the opinion that the difficulty for the phrase is only made salient as certain parts of speech. Having a compound noun as a direct object introduces ambiguity: “She had many gin(s) and tonic(s).” What the writer wants to say is that she had many drinks each of which happened to be a gin and tonic. Thus, the phrase should be hyphenated to demonstrate that the phrase is one object of the verb: “She had many gin(s)-and-tonic(s).” But now, in this use, it would be very strange to say, “She had many gins-and-tonic.” Because the whole hyphenated phrase needs to be pluralized. Therefore, I suggest that in a case where the compound phrase serves as a discrete part of speech (such as a DO), we ought to say “gin-and-tonics.” If we can form the same phrase in another way not necessitating the hyphens, then perhaps we can move the plural ending.
Who care’s about grammer when your drunk? Hic!
Hope this Grammar Police Deputy is not drinking G&Ts on duty :-).
Where can we take this test on gin-and-tonics? Would it be a taste test? Seriously, we agree with your tendency toward hyphenation.
Whoppers Junior or Whopper Juniors?
Is it visitors’ parking or visitor parking or visitor’s parking? Help!
We would say it could be any of these, depending upon the context. You could use “visitors’ parking” if referring to a lot of multiple spaces. “Visitor’s parking” is appropriate if it marks one space only. We recommend the safest bet … “visitor parking” for almost any situation.
It is for a large corporation with multiple spaces. Thanks Carol
You’re welcome, Pamela. Our suggestion is to use “Visitor Parking”. Please send over a photo when you have your signage done? Thanks.