I was looking at my reputation timeline graph and I wondered about a spike of 164 rep I'm sure wasn't there before. Upon looking it up, I found an entry +100 : association bonus
Does anyone know what this is awarded for?
You got +100 for associating your account with your account on another SE site. This is for getting users to connect their accounts in the network.
That's why you often can see users seeming to start with 101 rep, not just 1.