I have found the best option for reasoning with the wife is to say "it is to make the bike safer to ride" or "the old one is broken". They alway's like to hear you are looking after your self by making it safer....
Just like when i ordered my D&D's, I said "loud pipes save lives"

TBA, Stainless extractors / drag pipes, 65mm over forward controls, Thruxton needles, 904cc, head ported, lowered 1-inch, Console removed, relocated battery box, Australia.