As most of us have heard (and some people get offended about), there are dialects of English in which the word ask undergoes metathesis and is pronounced aks. Are there English dialects in which this process is productive and replies to other words? That is, do some people who say aks for ask also say flaks for flask, deks for desk, etc?
Take a look specifically at this subsection in the link @John Lawler posted: "Phonological History of English Consonant Clusters: S-Cluster Metathesis" at en.wikipedia.org/wiki/Phonological_history_of_English_consonant_clusters#S-cluster_metathesis:
S-cluster metathesis is the metathesis of final consonant clusters starting with /s/ occurring in African American Vernacular English as well as many other varieties of English "For AAVE speakers with S-cluster metathesis the following words can undergo the following changes:
ask → /ˈæks/
grasp → /ˈɡræps/
wasp → /ˈwɑːps/
gasp → /ˈɡæps/
S-cluster metathesis is lexically determined.
I have to reject your premise that these people "metathesize" ask. They do not. "Aks" is the standard pronunciation in their dialect, and has been for generations. It has undergone metathesis at one point, that much is true, but that was a thousand years ago, and they are not even aware of that.
Unlike children who try to say "spaghetti" and end up saying "pasketti", these people do not try to say "ask" and fail. Much rather, they actually want to say "aks" and then do just that. (Just like when you say "thirteen" — it's not like you are trying to say "threeteen" and failing.) Metathesis would be if they actually failed to say "aks" and ended up saying "ask" instead.
This is a training issue. People who have not trained themselves or been trained in school to enunciate the word "properly" say it in a manner that is more natural to the tongue and easier on the muscles.
Another word like this would be Youths - mispronounced like utes by many with a Brooklyn style accent.