Pull the battery and do a NANDroid back up. To do a NAND backup, boot into recovery (turn off ur phone, wait 20 seconds, press volume down+power, wait for the phone to scan some files) press volume down to go to recovery, press power, go to back up and restore. From here, if you choose back up, you will back up the CURRENT rom you have on your phone. If you choose restore, you will get a list of nandroid backups that you have made. Before this, however, go to wipe factory data and wipe it. Then go to cache data and wipe it and, lastly, go to advanced and wipe dalvic - YOU MUST DO THIS! Sorry, didn't mean to scream...
Assuming your buddy knew what he was doing, then you should have at least one back up - a copy of your original stock rom - in a "year.month.day.hour.minute.second" format. If you choose this rom (highlight it using vol up/dwn and press power) then you will be asked if you want to restore it. Go to yes and let it do it's thing. When it's done, go to reboot and now you'll be back at your original rom. Download Titanium Back up run a batch and restore all of your apps.