Lyric discussion by Paega 

blue_meanie I agree it's a wistful rememberance of cruising in his youth, and "I forgot my shirt" and "recklessness" a reference to unprotected sex in the era before AIDS. It's why 'nightswimming' deserves a quiet night, somewhere away from the crowds for "fear of getting caught". The photo on the dashboard, illiminated by streetligts, shows him his younger self, causing him to remember his youth; "september's coming soon" is an acknowledgement that he's approaching middle-age.

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