Let's be honest, not everybody is meant to be a creative. You may be creative, but that doesn't guarantee you a position in an agency's creative department.
Fret not. There are so many other positions for you in an ad agency. You can still be a part of the process and enjoy wearing jeans and tattoos almost every day.
Here is some quick info about other positions in a ad agency, perfect for a range of creative types.
Account Manager
Business side. Deals with clients directly.
Account Planner
Psychology/Cultural/Strategic side. Deals with the target market.
Media Planner/Buyer
Media side. Deals with where, when and how ads will be. What TV shows, what websites, etc.
Project Manager
All sides. Deals with creatives, account team and production to keep everything on time, in budget and running smoothly.
Social Media Strategist
Social media side. Deals with brand's online presence.
These are just a few. Go to mediabistro, Talentzoo or other job sites and check out the job descriptions for the above and more, you might find something that excites you. And, you won't have to make a portfolio!