Interpretation: People with teeth-rich smiles aren't always smiling. But when Gemma was smiling with her mouth open wide and flashed her pearly whites, the smile made her seem friendly. What’s more, she was waving to people at the same time, which made her approachable and indicated her willingness to being introduced.

Interpretation: Although Meadow showed a smile, the smile with the corners of her lips appearing tightened indicated a mixture of disgust and resentment. Coupled with her having the arms crossed, the nonverbal behavior set indicated her unpleasant and impoliteness towards Tina.

There are direct and indirect ways in which somebody is impolite. The direct ways including dismissals, silencers and threats. And sarcasm is an indirect way. 

Gesture: Gemma turned her body towards the person she was talking to, gently bowed and stretched out her hand first.

Prosody: A rising tone.

Interpretation: It might be hard to assess the overall politeness of the conversation simply according to the intonation. But together with Gemma’s friendly body language and polite greeting gesture, the overall conversation was conducted in an enthusiastic and friendly way. 

Gesture: Meadow was talking with her arms crosses and was rolling her eyes.

Prosody: There was a significant rise-fall tone.

Interpretation: The intonation pattern Meadow used might just indicate her disagreement. But together with her crossing arms showing defensiveness and rolling eyes indicating disgust, the way Meadow talked to Tina could be interpreted as impolite. 

Gesture: Meadow used her index finger pointing at Tina but opened her palm to refer to Gemma. And she was raising her eyebrow while talking to them.

Prosody: A raising of voice (including raised pitch and loudness).

Interpretation: As mentioned by Culpeper, the raising of voice can be regarded as a prosodic device used to manifest impoliteness. Meadow’s invading the space of Tina, together with her rude gesture of pointing at Tina were obvious impolite behaviors. However, Meadow’s “polite” gesture towards Gemma in the context could also be interpreted as mock politeness if the gesture and prosody were observed as a whole.

All participants say a lot and respond to others. And Dave and Jemma are obviously voluble, their volubility can be considered as an involvement strategy.
③ Notice or attend to Hearer: 

④Indicate Speaker knows Hearer’s wants and is taking them into account
[Look, if you like those spanx, you're gonna love these cashmere scarves]

Gemma told Tina that [you are being profiled]
③ Claim common point of view:
Tina agreed with Gemma and said [OMG, Gemma, I think you might be right]