Microsoft doesn't tolerate any sort of modifications anymore. When caught they will always ban you. This wasn't a 'Stupid' reason, they caught you manipulating the content they offer you.

Yea you get insta banned when messing around with your account.
Well now you know.
its not worth being banned until 9999

Although this is something petty, you still took it upon yourself to mod your avatar with 3rd party software - something that Microsoft don't condone - and now you're feeling the consequences of your actions. People learn from their mistakes, so hopefully you do, too. Don't make the same mistake twice. As for the ban, anyone should know that Microsoft do not show any leniency toward people who manipulate their software or products. Especially considering that very few people hold the licence(s) to Microsoft's software, which makes it eligible for them to change.

Modding your avatar? Haha I got banned for the same reason!

I got banned for the same reason in 2011. I was mad because had $600 worth of game/dlc on that account that wasnt installed on my xbox. We all learn from our mistakes.

dont worry buddy your not the only one....

This is kind of a dumb reason, but you did mod your avatar and it is against the terms of service. I think since so many people get banned for this they should just add it into the avatar options.

ive had a red avatar for almost 2 months now and 8 years on my account and still havent been banned
might take it off now

If you violate the xbox live code of conduct you always have a chance of getting banned. :/

It's against the Code of conduct, what did you honestly expect.