I can't excuse Lois, but its actually rather common that you cannot recognise someone if they are dressed differently and if you encounter them in a different situation. Humans have a vast array of looks, but predominantly they fall into categories and groups. Even between different families there are people who look very alike. Heck films use them all the time as stunt doubles.
Take the vast legions of Elvis Impersonators as well.
The key isn't just that Clark Kent wears glasses whilst superman does; its that he also wears a different set of clothes, his bearing of his body shifts (Superman is standing tall and proud, Clark is just standing, sometimes even looking meek and withdrawn); the style of his talking, the conversations and the way he looks at a person, addresses them and engages with them.
One might think Clark looks like Superman a bit here and there, but their behaviour and all are so different that the mind easily identifies them as two separate people.