Shyer than the Sleeves on a Vest

Informant:

I had a conversation about proverbs they had learned from their families with three female employees at a local taco shop during one of the less busy times of the day.  Mercedes Rodriguez, 42, Maria Lopez, 23, and Rosalba Valdez, 18 each consider themselves Mexican.  Rosalba was the only one born in the United States, though she is a second generation immigrant.  People used to say the following proverb regarding Maria because she was shy and did not like to go out much.

Text:

Es más corta que las mangas de un chaleco.

Transliteration: She is more shy than the sleeves on a vest

Translation: A person who is shy will always stay away from social gatherings

Analysis:

This proverb comments, in a slightly negative light, on the behavior of those who are extremely shy.