In this scene, Heatwave is still having difficulties understanding human customs, such as 'summertime fun', and he certainly doesn't see the point behind the cheesy inflatable duck-ring he's had to wear to appear funny and entertaining for the children at the swimming pool (And yes, he still has to pose as a simple robot, as do the other team-members. ).
Whereas, Blades has been having a wonderful experience, hence the homemade Hawaian outfit.... I still don't know why I drew that! Cody even helped him get a date for the rest of the summer.
Plus, Optimus has had the most experience with earthly habits. That's why Heatwave has gone to him for guidance so soon. X3
(MAN! This took so many hours. For any of you who've been wondering why I'm so late.... This is why. )