Sack
You keep your substitute clothes in a sack. The clothes in the sack are just substitute clothes, so they only come out in emergencies.
Look at this sack of substitute clothes. Imagine it filled with all the clothes you hardly ever wear. What kind of clothes would be inside this sack?
たい
ふくろ
None
You need your substitute clothes so you take out your substitute clothes sack. You open it up to grab your substitute clothes, only to find out that there is a ton of salmon roe inside your sack. Oh man, you forgot all about putting that in there. You yell: F**K ROE (ふくろ) because that roe destroyed all your clothes and made it nasty.
Imagine how nasty it is in there. Also imagine how smelly it is. Feel angry about putting roe in your sack. Why would you even do that? Why would the roe do this to you, as well.