I just don't get it...

Sometimes I really don't understand, how come people like to drive SLOW when they are in the fast lane and drive FAST when they are in the middle or the right most lane. I was at the left most lane a.k.a fast lane this morning, i was not driving very fast, maybe 80-90 like that, then there's this car on my left switched on the right signal trying to cut into my lane. As a good driver, I slowed down a little bit and let the driver switched to my lane, right in front of me. Then the nightmare begins...

After she switched to my lane, she drives really slow...maybe 40...what's wrong with her? When she was at the middle lane, she drives as fast as me and now when she switched to the fast lane, she decided to go slow?

Argggggg.....