Passed on by Karen Chung on Facebook, yesterday’s Daddy’s Home:
Pass mustard for pass muster is in the Eggcorn Database; it substitutes a familiar lexical item for a less familiar one (in this case, in an idiom). Semantically, pass mustard has the advantage over pass muster by consisting of familiar items, but the contribution of mustard to the meaning of the whole is not at all clear, so this looks like a demi-eggcorn.
The cartoon has another extension of mustard to the territory of muster, this time for metaphorical muster ‘summon up’ (with direct objects denoting feelings, attitudes, or responses), originally based on the military verb muster (as in muster troops). Again, it’s hard to see how mustard is a semantic improvement here.
