New dry humor joke format! Help us figure out the formula!

So my boyfriend and I were sitting around talking, and he confessed to having a sudden boner, to which I tried to explain why I couldn't tell through his pants, but instead the conversation went like this:

Me: "I've never seen a boner through pants before"
BF: "Why's that?"
Me: "Because everytime I see one, the pants immediately come off."

In short, what I said had come out completely different to what I had intended, but much to both of our humorous delights. Immediately, he started making statements similar to the silliness I had just said, and after composing myself from being doubled over in laughter, I later joined in. The following are some of the jokes we came up with, and now we're trying to figure out the formula (note: these are to be read in a dry humor/Stephen Wright style)

I've never had to do laundry

Why's that?

Because every time I have dirty clothes, I just wash them

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I've never run out of gas before

Why's that?

Because every time I run out of gas, I just fill'er up

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I've never had to get the mail

Why's that?

Because every time I have mail, the postman delivers it

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I've never had cake this good before

Why's that?

Because every time I do, I eat it

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I've never had to cool off before

Why's that?

Because every time I'm hot, I just turn on the fan

Can you figure it out? We've already concluded that one of the components seems to be mockery of the listener's stupidity in expecting a contradictory response. Sometimes there's double-meaning, but overall, it seems to work best with the speaker talking about having never taken some sort of action, especially in tasks that are considered run of the mill. All other nuances for how the joke works is lost on us at the moment. Help us figure it out, redditors. :)