Otis.....in one of the finest episodes for one-liners.
Who said "I'll come!" and where was it said?
Sounds like maybe Goober?
I think you are right, Bernie, and it was when Andy, Helen, Barney and Thelma Lou were going to the movies and Goober tagged along.
...or was it Nurse Mary to Barney?...when he offered to take her to Rafe Hollister for a shot?
Yes! Goober and the Art of Love. Another Gooberism is "Say it again".
Who said "I'm a giant when it comes to potting petunias!" ?
I love that line. That's Andy to the boorish Roger Hanover, not long after Roger "helped" Andy fix a lamp.
Of course, Roger thinks he might get a hand in those petunias yet......