Mary takes a position as a secretary at the church. However, she quickly finds her role expanding when Pastor Jeff (Matt Hobby) begins using her as an unofficial marriage counsellor for his relationship troubles with his wife, Selena.

The central comedic engine of the episode revolves around a misunderstanding of the word “dthrip.”

The episode kicks off at a church potluck where Mary Cooper’s potato salad is a massive success—at least compared to her rival, Pam Staples. This success catches the eye of (played by Matt Hobby), who offers Mary a full-time job as the church secretary after the previous one was sent to rehab.

Missy uses George Sr.'s whiskey for sterilization during Sheldon's "surgery".

The episode you're referring to is likely Season 1, Episode 14, titled "David, Goliath, and DTHrip."

In this episode, Sheldon and his friends go on a DTH (Dungeons & Dragons, Tabletop, and Heavy Metal) trip, which leads to some interesting and humorous situations.