Speak for yourself
Definition 1 of 3
Pro Tip 1/3Personal Disagreement
Emphasize that you don't share the same opinion or state as someone else. 
She said we were lost, but I responded, 'Speak for yourself, I know exactly where we are.'
Pro Tip 2/3Colloquial Retort
Use it in a casual setting to counter a generalization made by someone. 
When he claimed all of us were vegetarians, I had to say, 'Speak for yourself, I love steak!'
Pro Tip 3/3Assert Individuality
Use it to stand out from a group that you've been lumped in with. 
When she said we all failed, I said, 'Speak for yourself, I passed with flying colors!'