Thank you, this is a very clear reply. I think I'll stay human then.I'd agree with them not taking people seriously if they play a draenei DK as there are races out there who give you a far higher advantage over other places. But I wouldn't turn down a night elf DK if they know how to use the racial properly.
To be honest it really depends on the server as well. For example on the realm I play with (a highly competitive realm), I think you will have trouble finding partners if you decide to play a draenei DK rather than any other race.
PvP is far different from PvE. Even though certain racials can give you a slight edge in PvE (some more than others) it usually isn't really a deal breaker.
For PvP it's different. If you manage to do a lot more pressure during the opener due to racials, you'll be able to force more CDs used as well which means you can push out more pressure throughout the game. If you manage to outlive CDs due to one racial, it means you won't have to use other CDs in order to survive, which again means you can endure more CDs later on or use CDs at different times.
Other racials give you a higher advantage vs certains classes like wotf, orc stun resistance or shadowmeld.
If you don't have to use your trinket for fear it means you can use it for a different CD (Take warrior for example. If you use wotf on a warrior fear instead of your trinket, it means you can use your trinket on a stun after 30-45 seconds).
Then we have draenei. They have a measly healing CD which doesn't really help much in most situations since it's diminished by battle fatigue.
The above reasons are the reasons I would rather take a human DK or a nelf DK or even a gnome DK above a draenei DK. Especially when playing with more inexperienced players who usually do not really know what to do in most situations.
I'm not trying to say: "don't play draenei" but I'm just telling you the reasons why people would be skeptical of playing with a draenei DK. :P