I think you should always respect personal boundaries, but it's precisely with those whom you are closest that you feel comfortable tinkering with those boundaries. If you never pushed the boundaries, you wouldn't have gotten so close to begin with. But once you find them, you never intentionally cross them too much - that would be a breach of trust.
[Edit] I write a little about the topic of play here: https://goo.gl/jHuUQn