I tend to go for the easy, childish options, like "Sarkozy, p'tit zizi" (Sarkozy, littl' dick, with word-pun on the -zy/zi).

I also came up with a few childish slogans for Ségo(lène) Royal, though not yesterday but a few days before that, when discussing the CPE with friends:

"Ségo c'est pas macho" (Ségo is a non-macho choice)
"Ségo c'est plus rigolo" (Ségo is a more fun choice)
"Ségo c'est pas Sarko" (Ségo is not like voting Sarko)
"Ségo c'est plus fort que toi" (derivation of a 90s cult French advertising line for Sega: "Sega, it's stronger than you")

But my adversaries were as likely to appreciate those as Bush is to regret invading Iraq, so it was to no avail.