Because your a 50, you need a name that will scare people, think of a name (e.g. Chaos) and make it pro, add more x's and I's and add other words as well, and spelling the word wrong with the same phonics. Also alternating the words with lower case and upper case letters such as xX iTz KaOs v2 Xx, or my old one, iTz CoBrA v2. Just a small suggestion.
SOmething simple and memorable, like that guy from MLG "Lunchbox" now that is an awesome name. How about, Hard Nipples. lol Nah, cant think of much right now.
chillin villin a guy with a hammer (you were beat down by a guy with a hammer) a guy with a sniper (you were sniped by a guy with a sniper) Chief Wiggum 00
Here's a not so serious one: You (You killed You) Idk about these but they may be good: ZOMGthekiller (try to make people say ZOMG like an actual word) -or- IronClad -or- ZCarpshwacker (idk, something random)
Try something that sounds slightly latin or foreign....usually that kind of thing rolls off the tongue and, well....really just sounds cool. Failing that, just use a word or a variation thereof that isn't used often. Praxius, Requiem, Viator Mortalis, etc. Combinations of words could also work out quite well, if planned out correctly. I'll post some more suggestions at a later time, when I'm more awake.
Try using 'Titmar' as your gamertag. It's very original. Or you could go with a random object, like 'lamp shade'.
A good way to make a gamertag is take a character from a game and mess with it or make a compilation of your own name...or BOTH