It's probably the joke that sums up Family Guy the most. A nonsensical fight with a giant chicken that lasts a sold 20% of the entire half hour episode. It's without explanation or purpose, but then again, so is most of Family Guy, so that's why it fits in so perfectly. 

A close second would be when Peter hits his knee and begins wincing for a solid three minutes, but that only happened once, but the giant chicken saga is a much richer tale overall.

Here they all in all their glory. Three more below continuing the epic struggle of fat man vs. giant chicken. 

 Round 2:

Round 3:

Round 4: