I'm assuming you're asking about removing yourself from an entire HIpChat Cloud instance - i.e. deleting the account associated with your email address. Head over to https://www.hipchat.com/account/delete - you'll sign in with the email address and password for the team you joined by mistake.
The web interface will require you to type your password again to confirm you really want to delete your account.
After that, you're free to join the team you meant to join with your email address.
...have mention name FirstnameLastname. Fe.: @MaartenCautreels This certainly helps to know who is being mentioned in a conversation. Imagine your colleague sends the following message...
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