
The only rule is: These must be actual reasons/excuses you have used on people. Let's not get too serious with this - these are purely for comedy sake.
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I'll get us started.
To justify to my roommate my first gun purchase, a Sig P226:
"To make sure you pay me your rent on time"
My response to explain to a girl friend when she asked why I needed so many guns:
"How many purses do you need?"
To justify to myself buying a second gun instead of just one as originally planned during a visit to Sporting Arms in Lewisville:
"Dude, it's reverse two tone"