1) The process of making something illegitimate
2) The process of bringing something to a form which is not as good as the one it was in before, i.e. the language glorified by urbandictionary.com
'fo shizzle my nizzle' is a bastardization of 'fo sheezy my neezy' which is a bastardization of 'for sure my nigga' which is a bastardization of 'i concur with you whole-heartedly, my african-american friend'