Especially on mobile devices, when a UI element repeatedly avoids or dodges your attempts to reach or interact with it. May be intentional or unintentional, usually a consequence of elements wrapping to the next row as you drag one element around. Notable examples include rearranging icons on the home screen and trying to push a tab into a tab group on mobile Chromium-based browsers.
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Nyah-nyah Effect (taken from the you-can't-catch-me schoolyard chant that goes through my mind whenever it happens)