They can be grouped in following two broad categories:
1) Those who are always looking for the next best thing, due to some underlying issue that prevents them from forming a long term relationship. OR,
2) The ones who have a Peter Pan complex and just never want to grow up.
Most of these toxic bachelors seriously consider settling down once they have a mid-life crisis and see the writing on the wall. Then they try to get married in a hurry to have kids, and to ensure their own immortality through their offspring.
*40 is a race-dependent number. Asians can be considered toxic bachelors if they remain single past 31.
Toxic Bachelorettes come in all shapes, sizes, and socioeconomic backgrounds, but share a common trait of wasting their prime mating years in a futile relationship with a guy they chose for the wrong reasons. (E.g., "I only date someone who uses colorful toothpaste, or answers his phone with 'Ciao'.")
Most of these toxic bachelorettes are fueled by pre-menopausal hormonal imbalances, and hate men in their age-group while constantly seeking affection from far younger men.
Ann Coulter is a toxic bachelorette according to Wikipedia.