Since this is about excuses, my absolute number one is:
"It was
super cheap, I mean fifty bucks? The derailleurs alone would get that on eBay!"
And then the flip side of that coin (like Robbie, above):
"Yes dear, I just paid $500 for that bike, but you should be happy because I just sold
three other bikes to fund its purchase."
Heads I win, tails I'm victorious.