Chapter 3: page 45-46 "Well he seen this girl in a red dress. Dumb bastard like he is, he wants to touch ever'thing he likes. Just wants to feel it. So he reaches out to feel this reb dress an' the girl lets out a squawk"
Lennie was attracted to the dress because it was pretty, red and soft with the underlying level of him being attracted to her femininity, like a little boy accidentally pulling a girls pig tail. The girl doesn't know what to do and screams out of fear and the possibility of her self being hurt for her femminitnity since her dress, as very feminine thing is what her targeted.
A tart is an old expression for a woman who "gets around a lot or gives the eye." In this case Curleys wife has been giving everyone the eye at the ranch including George and Slim. This might be one reason why Curleys so antsy, and wanting to fight everyone. Curleys wife is a good stereotype for a slut.