Basic Trope: A character learns and grows by the association of wacky friends.
Straight: Bob learns to become more social thanks to Alice and her eccentric friends.
Exaggerated: Bob becomes extraverted thanks to Alice and her Cloudcuckoolander companions who turn out to be aliens that take him on wacky adventures.
Downplayed: Bob learns to take things less seriously after he becomes friends with Alice who has a unique hobby.
Justified: Bob was horribly depressed due to having few friends but the sweet and fun nature of his crowd of new friends cured him of his loneliness.
Inverted: Bob becomes asocial due to being around boring people.
Subverted: Alice and friends try to get Bob to break out of his shell, but the extra craziness causes Bob to retreat even further into his shell.
Double Subverted: Bob eventually opens up to them once they back off and he misses them.
Parodied: Bob is extremely boring and mundane until he befriends Alice the Clown who constantly pops out of nowhere to liven things up.
Zig Zagged: Bob was boring until he joined (or was roped into) the crazy crowd. He begins to loosen up, but it's a ruse to make them go away. When they do, he misses them and joins in but makes some boring-guy excuse.
Bob becomes social by being around normal and level-headed people.
Bob remains an introvert no matter how many times has he been around Alice and her friends.
Enforced: The writers realize Bob is a boring character so they gave him a wacky friend.
Lampshaded: "My life was so much more boring until I met you."
Bob hangs around crazy people hoping that it'll help him loosen up.
Alice and friends act crazy around Bob, hoping it will loosen him up.
Exploited: Bob's therapist introduces him to the crazy crowd hoping that they will loosen him up.
Defied: Bob recognizes the looney friends as looney friends, and stays away from her, content in his lonely existence.
Discussed: Bob and Alice's friends discuss how much more fun Bob is now that they know one another.
Conversed: People watching "The Bob and Alice Show" talk about their relationship.
Deconstructed: Alice and her friends' eccentric behavior drive Bob away and he stays away. If he wants friends, he'll find ones more mentally stable ones.
Reconstructed: Alice and her friends are a professional comedy troupe and Bob is their Straight Man. He warms up to them eventually, even drinks with them after work, but spending more time than that with them is exhausting.
Played For Laughs: Bob, the Comically Serious, is constantly befuddled by Alice's goofy hijinx.
Played For Drama: Bob was suicidal and the lively nature of Alice and her loony friends helped enable him to overcome depression.