According to urbandictionary.com, a flaker is:
1. A person who bails out on a commitment at the very last minute.
Example: Jane is such a flaker. I can’t believe that she bailed out the very last minute! I’m definitely not inviting her to hang out next time.
2. Someone who flakes.
Example: You flaker. Why did you bail at the last minute?
If the following applies to you, then you suck big time =p