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cursor dipped in X: n.

There are a couple of metaphors in English of the form ‘pen dipped in X’ (perhaps the most common values of X are ‘acid’, ‘bile’, and ‘vitriol’). These map over neatly to this hackish usage (the cursor being what moves, leaving letters behind, when one is composing on-line). “Talk about a nastygram! He must've had his cursor dipped in acid when he wrote that one!