Depending on the personality of the person who is asking, you could use the opportunity to spin a huge shaggy dog story.

It doesn't have to be true, but a good story should have enough elements of truth to be at least vaguely plausible.

 * [TV Tropes](http://tvtropes.org/pmwiki/pmwiki.php/Main/ShaggyDogStory)
 * [Samples thanks to the subreddit](https://www.reddit.com/r/ShaggyDogStories/)

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Example:   

> "Well I on my way out the door yesterday when I couldn't find my car/bike key.  You know I live in Outer-Rotovegas and there's no public transport, taxis and ubers just don't want to go there, and walking would take all day."    
 
> "So I had to find my keys.  I searched everywhere, the bowl of keys, the keyhook board, all my pockets in all my clothes, in and under the washing machine and drier/line etc."

> "Then it started getting serious.... I started moving furniture, looking inside books and potted plants.  I even searched through my late grandad's key collection which is 47 filing cabinets filled with historical keys dating back to ancient Egypt, no dice!"    (Continue in this vein, but keep making references to details that can be corroborated)

> "Finally I'm about to start tearing up the floorboards in the kitchen with a crowbar, and I heard something odd... it was a faint jangle of my keys!   But where was it coming from?   You know how a sound can be all around you and not have a discernible direction?  It was like that - no matter what way I turned the sound came from behind me."

> "It was exasperating!  So I grabbed a kitchen chair and sat down.  It was really uncomfortable behind my back, and when I took my jacket off there were my keys, hooked into the material between my shoulder blades."

> "By this time it was 17:00 and not even worth coming into town cos I'd spent 8 hours finding the sodding keyring!"

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If you want to be harsh, this is a lie.  However its such a whopper of a tale that takes a long time to tell, and that you tell it with a straight face.

Story would be more amusing if you lived right-close to work and the disparity between reality and story make it incongruous, which is funny.