The frog in the video is showing it's threat display which it would use towards a predator. I've never seen one that aggressive before but they all have their own unique personality. And as you can see during the end of the video, you do NOT house these guys together. They can and will injure/eat each other.
The "teeth" you are seeing in the second video aren't true teeth but an extension of the jaw bone called an odontoid. They act as teeth and help the frog grip the prey.
I don't have a Pacman but I do have a Pyxie Frog which is it's larger cousin. Mine is sadly only a female but I still would not want to get bit by her!