What should be an exchange of names and notification of injuries, or illness, has somehow turned into this:
"I'm no good."
It's silly that students feel they need to say these words to disclaimer their practice, as if lacking strength or flexibility gave them less entitlement to be here. That's why you're here.
"I can't do such-and-such posture."
Just because your posture doesn't look like his posture doesn't mean you aren't doing it. In yoga there is no "doing" there is only "trying." The trying is the doing! Your body benefits therapeutically when you try the right way to the best of your ability. Who cares how you look, how do you feel?
As in, about my performance..? I used to say this to a teacher after a class if I had to sit down during the class or if I felt my postures that day were worse than usual. Yoga isn't about doing 110%, it is more important to focus on your body and where you're at today, and sometimes that means doing less or taking breaks, whether that's every class or once in a blue moon. It is also good for newer students to see other students look after themselves properly so they know its okay.
Please don't feel like your teacher or other students are discounting you because you sit down, fall over a lot, or can't touch your toes. Realize that you didn't come here for any one else or to prove anything. Learn to be thankful for your practice instead of self conscious or sorry.
Ask yourself if yoga has enhanced your life. If the answer is yes, then forget all the rest!