You can't pick my brain because my brain doesn't work like that. If you want information from me, you are more than welcome to get some. In fact, I'm an open book. I love answering questions, I love making time for people. But there's a right and wrong way to do it.
Asking if picking someone's brain is the wrong way. Messaging them out of nowhere on twitter or Instagram and saying “Hi, can you invest in my startup” is also the wrong way. Finding their mobile number and calling them at 1AM is also the wrong way (It's happened).