So you might have one of those friends who just likes to play with the lock pattern on your android phone. And then he/she might enter a wrong pattern 20 times! What happens as a result of this is not pleasant. You will be asked to sign in with your Google account. But that won’t work. You will repeatedly see this message: “Invalid username or password” even though you are sure you are entering a correct username and password. I tried different solutions given on youtube and other forums but none worked. Well except one where a “sucky” but working solution was provided. By sucky I mean having to factory reset your phone. That seems to be the only solution.
To reset your phone these are the steps. (I speak on behalf of Samsung Galaxy Pocket S5300 only though)
1. Power off your phone.
2. Press your volume-up button, your home button and your power button till your System Recover Screen comes up.
3. Scroll down to “wipe data/factory reset”and press the home button to select this option.
4. A confirmation screen comes up. Scroll down to “YES — DELETE ALL USER” and then press the home button.
5. Select the “Reboot System Now” option next and wait for your phone to reboot.
Your phone will then boot with all data wiped and all settings reset. At least you can use your phone after this. If anyone has any better solution do post your comments. Cheers. ;)
Do refer to this documentation provided by Google as well. [Edited June 22, 2013]