Riding a borrowed bike Thru Mexico into Guatemala.
 

I'm borrowing a bike from my USA buddy, anyone think it will be a problem doing the above trip? Does the bike need to be registered in my name?

Yes and yes. Don't count on crossing a border with a vehicle registered in someone else's name. Contact the relevant embassies and ask whether they will accept some kind of authorisation document. Change the rego, if you can.