This particular stroll usually takes place after a night on the town that involves heavy partying and you can recognize these people as they are either in “club clothes”, clothes belonging to people that they slept with and/or carrying their shoes from the night before.
The First Kiss video went viral and was watched +40 million times on Youtube in barely 5 days, needless to say that parodies are popping up everywhere now, including this dirty one.
There's also this one with dogs, called First Sniff.
And this one supposedly authentic, called The Real First Kiss.
NSFW for obvious reasons