Demonic roulette
You can summon a demon and you can choose your name, but you can't choose your summoned demon's name. Unlike hunters, warlocks don't get to name their pets. Instead, their demonic names are randomly generated from a combination of syllables. Blizzard says this is because demons have their own names when they're summoned, whereas animals get given names by their human owners. Warlocks share their best and worst demon names in this thread, which includes such gems as:
Chopit, Rubtip, Awang and Karrot the imps
Grimthang, Bigmooth, Kraknutz and Krak'ho the voidwalkers
Hellina, Angora, Vigana and Bro, the succubi
Kuushion, Shaaron and Phuukum, the felhunters
Some pets, such as Vigana and several voidwalkers whose name ended in "nutz", were actually reported to the GMs for obscene names. The GMs mostly let this go, although they did change the name of an imp named Karpet because people kept /licking it.
What's the best demon name you've seen? Do you wish you could "name" your demon or pick its name from a list instead?