People who invest heavily in their running (financially and emotionally) yet won't join a club. These people are useless to the sport IMO. May aswell be playing tennis or judo as they are keeping themselves (and their money) outside of the sport, when the sport badly needs them (and the money). I'm not talking about people who are starting out. I'm talking about people who have been running for a good while but full on refuse to join a club despite being perfectly capable runners.
The closest club to me is 15 miles away, where the membership is predominantly female whose only goal seems to be to loose weight and compete in the DCM hoping for a sub 5. Generalisation I know but this is the reason I'm a solo runner. Plus if people in clubs share your attitude I don't think I'm missing much tbh.