He nodded at Xander's assessment of Jessica. "Long, dark hair. Likes to wear leather and jeans." Sherlock couldn't care less what Jessica liked to wear -- she could wear whatever the hell she wanted to wear. Sherlock wasn't about to judge her for her choice of clothing.
Of course, if suddenly she started wearing skirts and pink and frills, he was going to question it. Just not judge her on it.
"Nice to meet you, Xander," he said, trying to be polite. "I am Sherlock."