Check under the Chart dissplay window, one option is there Excluded column.
There your column is available and then drag and drop into slice section.
The chart building interface has changed as we move from 10 --> 11. You can still slice by a metric but you must drag and drop the columns to the Measures > Slice Size section.
I tried to slice by measure by dragging the column to slice size section. I have 3 metrics PO Under Count and PO Over Count which add up to total PO count. So I want my pie to ahve 2 slices one for PO Under Count and other for PO Over count. However when I drag the 2 metrics, it shows me 2 pies, one for Over and the other for Under count.
I am seeing the same thing - if I have a single measure column with each measure repeated in the ROW, I can create slices in the Pie Graph. However, if I have column measures where each column is its own measure, I cannot create slices, no matter how much I try. In OBIEE 18.104.22.168 you can't drag items in the Pie Graph definition windows out from the slice size box to the slices box.