It's not irrational if you know that the insurance company has mispriced your policy, and filing a claim won't be more trouble than it's worth.

Getting a contents policy in a safe neighborhood where you know that there's little risk is likely not a good deal. Getting a contents policy when you've learned that your neighbors are getting into hard drugs is probably a good deal.

Paying $19/mo for third-party full coverage + theft on your $1,000 mobile phone is probably not a good deal even if you know you are high risk, for the simple reason that at $19, they game must be that they will find any reason to refuse to pay, and will give you a poorly refurbished phone for your troubles if you make them honor the insurance.