Clue: Rumpy-pumpy with poor Kiki moving twice this fast (3,6)
Answer: YOM KIPPUR
Explanation: Definition: this fast
*(rumpy po ki) [anag:pumpy] where PO and KI are PO(or) and KI(ki) "moving twice" 
*If I have parsed it correctly, this is nonsense.- [edit – see comment no 2 below]