Similar to "this isn't where I parked my car", it's a phrase used during a fight or awkward situation
Facebook convo:

Person 1: I hate you you're a bitch
Person 2: Fuck you and die
Person 3: You're just mad because she fucked your boyfriend
Person 4: This isn't where I left my oatmeal...
by MuchoMoney August 11, 2011
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