It’s pretty discreet. The sender is listed as “Web Merchants, Inc.” and the customs declaration (if applicable) says that the package contains “manually operated massagers,” if I remember correctly.
If you’re super worried about your parents getting suspicious, the best solution would be to go to an actual, physical sex shop. Just make sure you buy something made of a nonporous material (i.e. no jelly, rubber, cyberskin, etc. - go for silicone, glass, steel, or hard plastic).