You may proceeded successfully and smoothly when jailbreak, installing tweaks is also a risk. If you happened to touched a tweak that is not yet compatible with iOS 6, it would make your device go into a endless boot loop. In this case restoring is not the only solution. MobileSubstrate features a failsafe to correct the situation. Take a look saving solutions from folks over iJailbreak.
After this ordeal I thought to myself that a lot of other people will likely be in this same boat and I should write an article explaining a couple of ways to fix a bad Cydia tweak installation without actually have to restore or re-Jailbreak your device. This applies if you cannot get out of safe mode, are stuck in an endless boot loop, have installed a pattern lockscreen tweak that has locked you out and pretty much any other problem experienced after a bad Cydia tweak installation.
Method #1: If you are simply stuck in Safe Mode then your solution is extremely simple. You will just need to launch Cydia, go into the Manage tab, then the Packages Section, find the Cydia tweak or tweaks that are giving you issues and uninstall them. Once they are uninstalled you can respring your device and it should be back to its normal Jailbroken state again.
Method #2: For those of you who are in reboot city and can’t get out of a boot loop there is actually a solution to the problem thanks to a recent update to Mobile Substrate from Saurik. When your device is rebooting hold down the Volume Up button and doing this will essentially cause Mobile Substrate to be disabled, which in-turn kills all of your tweaks temporarily. You can then launch Cydia, go into the Manage tab, then the Packages Section, find the Cydia tweak or tweaks that are giving you issues and uninstall them. Once this is complete reboot your device and make sure it reboots into a normal Jailbroken state again.
Method 1 or method 2 should allow you to fix most issues caused by a bad Cydia tweak installation. I know method 2 has saved me many times. Let us know if you have any other suggestions in the comments section.