Tell her it's not that embarrasing.

"How do you know that she's my mom?" you asked in a puzzled voice.

The sales clerk smiled. "I could immediately see the family resemblance," she answered. "And you clearly looked uncomfortable when you walked into the store. It was easy for me to guess."

You laugh nervously. "Uh, you got it. That's my mom. I promised to take her shopping, so..." you trailed off.

The assistants smile grew wider and she gave you an appraising look. "That's very sweet of you. Not many grown men would be willing to take their mother shopping for lingerie. Is she shopping for someone special? Your father perhaps? Or a boyfriend"

The conversation was making you more uncomfortable, afraid that you might give something away about your true relationship. "No, dad died years ago. And no boyfriend right now. Mom just wanted something nice, I guess."

She got a thoughtful expression. "So I assume you here on vacation with just your mom...do you want to meet for dinner tonight? I've got an uncle who would be perfect for you mom to meet - someone she could have a lot of fun with while your here." She paused and her smile grew a little sheepish. "Besides, I think I'd like to get to know you better..."

At that point Jackie walked back up with several items she had chose. She obviously caught the tail-end of your conversation. Your nerves were completely frayed by then...