labs <- expression( , NC==17, PG, PG==13, R)
ggplot(data = movies, aes(x = rating, fill = NA)) +
  geom_density(alpha = I(0.2), aes_string(fill = "mpaa")) +
  scale_fill_discrete(name = "mpaa", breaks = levels(movies$mpaa),
     labels = labs, formatter = parse) +
  geom_text(x = Inf, y = Inf, label = "Test", hjust = 1, vjust = 1)

# Annotation in top-right corner disappears
ggplot(data = movies, aes(x = rating)) +
  geom_density(alpha = I(0.2), aes_string(fill = "mpaa")) +
  scale_fill_discrete(name = "mpaa", breaks = levels(movies$mpaa),
     labels = labs, formatter = parse) +
  geom_text(x = Inf, y = Inf, label = "Test", hjust = 1, vjust = 1)