Carbs...delicious, readily available bread, pancakes, waffles, cakes. This weakness once led to an infamous donut eating contest at my first job (I lost). See, it's work related! For a more work-related answer...
As an Advocate (INFJ-A), I am driven by connecting and driving others to be successful. All strengths have a corresponding weakness. This comes at the expense of myself, where I neglect being assertive toward my own growth. I must make a regular, conscious effort to keep myself in mind - but it's not natural.
According to my personality type, I am likely to have irrational fears. Yup. Heights. Get me six feet off the ground, and I am uncomfortable. A ladder is the most terrifying invention I've ever had the displeasure to experience. Please ignore how my passion for traveling (often requiring a flight) doesn't bother me.
PAST
In the past, my weakness was "perfectionism". Thinking why does anyone think this is a flaw? I later learned how much this hurts delivering solutions. Waiting until things are perfect both makes it hard to get feedback early as well as perpetually delaying ever finishing. I enjoy coaching others through similar challenges and showing them how crude early drafts (like this website) are better than striving for perfection out the gate.
But also
Playing golf. I am a disaster both on the course and virtually. However, if you are looking for someone to make you feel better about your game, I guarantee I am worse.