I used to run a bike shop. Every time I would sell a bike, I would make sure the customer had a good discussion about why they should buy a $30 helmet. The $30 helmet was usually less than 10% of the bike purchase. When they would say "It's not comfortable", I would ask them what their head is worth. Maybe not to them, but to their family. If they had brain damage, what would their life be like? Could they still work? What would happen to their family if they couldn't? Once I sold a bike, and a helmet, to a bright kid who had a major head injury from a car accident. He had been a bright engineering student, after the accident he lived at home with his parents. He applied once for a job, but did very poorly on the math test (~ sixth grade skill level) we gave prospective employees. Head trauma can really screw up your life, so don't take the chance.
I've been in a number of bike accidents, one of which caused a concussion and an overnight hospital stay. No helmet. I've had some where I hit my head, and cracked my helmet, with no head trauma. If had more where I scratched my helmet, with no problems.
The rule with my family is the same as the rules at a triathlon: if you are touching your bike, you MUST have a helmet on.