Try something comical like 'An Armed Squirrel' or 'A Flying Refrigerator'. BE creative and come up with something great.
make it a random adjective then a random noun, but spelled a little askew. like a mad lib. or you could go with cuntsucker4life. jk
what i like to do in Halo CE, is name myself something like a bullet so it says "You got killed by a bullet" just try this FILL IN You got killed by (your text here)
Serious names: 5tunGunz Warz Rega1ia Mind of Chr0me D1ce n V1ce He11fire Srsly, that was off the top of my head. If you want to, you can replace numbers with letters, vice versa, letters with letters. If you're still trying to make up one yourself, I would avoid names that sound funny when you kill someone, because they don't make sense when you die.