Tipping a Server vs a Barista vs the DQ Worker

We got an interesting email based on tipping. Should you still tip 20% if the service is bad. Why do we tip baristas and not the DQ worker? Also we're looking for suggestions to celebrate a 30th birthday! Email <a href="mailto:ryanshow@kdwb.com">ryanshow@kdwb.com</a> if you have any!