Finch got revenge on Stifler by having sex with Stifler's attractive mother.
The Act of Revenge
On prom night, Finch not only achieved his goal of losing his virginity but also sought revenge on Stifler. His method of retribution was to engage in sexual intercourse with Stifler's mother, an attractive woman. This act caused significant chagrin and embarrassment for Stifler.
This particular action by Finch was a direct consequence of an earlier incident where Finch had been publicly embarrassed and left without a date when Stifler was present among a crowd of other students.
