Not everybody has the same taste in death-metal as you.
Not everybody has the same taste for the Bee-Gees as you.
Not everybody has the same taste for Country as you do.
Seriously, getting requests is the best way for the DJ to know and learn about what people like to hear at events. So bring them early and bring them often!
... but ...
Please don't be upset when we don't have time to accommodate every request. You also should consider that the happy couple(in the case of a wedding) or organizer has probably already given pretty clear directions to the DJ on what types of music to include.
We also consider the group as a whole when we make our play-decisions. Hip-hop is great when there are fifty 20-somethings on the dance floor, but when the grandparents of the bride are out, it is not such a wise choice.
Enjoy the music, and request responsibly!