Nouns ending in -ie are usually feminine.
The suffix often names an abstract quality, an activity, or a discipline.
Is connerie masculine or feminine?
laconnerie
The rule behind it
95.7% of -ie nouns are feminine
In context
La connerie est la décontraction de l'intelligence.
Stupidity is the relaxation of intelligence.
Sur Internet, la connerie a pignon sur rue.
On the Internet, nonsense is front and centre.
J'ai claqué tout mon fric en conneries.
I spent all my money on stupid stuff.