/hash kə-ˈli-zhən/
[from the technical usage]
n. (var. 'hash clash') When used of people, signifies a confusion in associative memory or imagination, especially a persistent one (see thinko).
True story: One of us [ESR] was once on the phone with a friend about to move out to Berkeley. When asked what he expected Berkeley to be like, the friend replied:
"Well, I have this mental picture of naked women throwing Molotov cocktails, but I think that's just a collision in my hash tables."
Compare hash bucket.