How much fan is too much fan?

The leaves on my seedling have curled upward (after being flat) and I was told this is a sign of bad ventilation.

I have a computer fan on it and want to know how much wind is too much?

Obviously if the plant is bending it's too much, but is it okay if it vibrates just a little? Vibrates a lot?

yeah you want the leaves to blow around a bit. I'd say if it doesn't blow the plant over, its all good