I would be quite happy to call Danny Alexander stuff far worse than a Ginger Rodent to his face, but the situation would be a long the lines of :-
- We knew each other well
- Had a beer or two
- We got on well
- We both knew the other would take a joke
Beer, Danny Alexander and Clive are 3 thing which will never go together. Harman's remark does demonstrate how relatively easy being in opposition is. You just need to disagree and fling mud of various sorts until you find something that sticks.
Having some sort of ministerial responsibility means having to make hard choices in situations that don't have a right answer. Look at Plaid's Elin Jones and the Bovine TB/Badger mess or Vince Cable and Tuition Fees. Both good people trying to solve intractable problems and getting it in the shorts from all directions. Opposition does not need to have a fully costed and risk adjusted alternative, they just need sound bites which have a veneer of principled justification.
I am afraid that the "Ginger Rodent" gag only demonstrated how hard constructive criticism in opposition really is, even at a Labour party rally.