Lorraine's mother does not want her to go to Stryker's Luncheonette because she is afraid that she will get in trouble with the boys that hang out there.
Stryker's Luncheonette is a favorite place for the teenagers in the area to gather. When Lorraine's mother asks her where she went after her drama-club meeting, Lorraine tells her,
"I had a soda with the kids afterwards at Stryker's Luncheonette."
Lorraine's mother gets upset, telling her daughter,
"I don't want you going in there. I told you that."
When Lorraine responds that
"All the kids go there,"
her mother comes back with the retort,
"I don't care what all the kids do. I don't want you in there. I've seen those boys hanging around there, and they've only got one thing on their minds" (Chapter 6).
The "one thing" that Lorraine's mother is speaking about is, of course, sex. Lorraine's mother is obsessed with the idea that men are evil, a reaction most likely to the fact that her husband left her when she was pregnant with Lorraine. Lorraine reads into everything her daughter does, imagining improper motives and behavior in all her relationships. Even in regards to Mr. Pignati, she is blind to all the real and important elements of her daughter's interactions with the old man, and only wonders if the Pigman has tried anything inappropriate with her.