In a GridControl, when you double click the border between column headers, the grid reset teh column width to the default column size. If you want sme other behavior, then you can handle the ResizingColumns event. Here is a handler that will do a resizetofit on a double click.
private void gridControl1_ResizingColumns(object sender, GridResizingColumnsEventArgs e)
{
if(e.Reason.Equals(GridResizeCellsReason.DoubleClick))
{
GridRangeInfo range = e.Columns;
this.gridControl1.Model.ColWidths.ResizeToFit(range,
GridResizeToFitOptions.IncludeHeaders);
e.Cancel = true;
}
}