This behavior is not ok.
It is a Monday morning. Were you aware?
I now realize why, when I was in high school, adults on the train hated my friends and me(!). At the time I thought "they" were ageist freaks! Now I know that it is the other way around: teenagers are little psychopaths trying to ruin my Monday. Technically I already knew this tried and true fact, but it seems like fresh information right now.
I will not let this ruin my day. I will move on and forget the inappropriate PDA that started my work-week. I will get a lot of work done. I will persevere. I will pledge to end the week with some PDA of my own.
Why should the teens get to have all the fun?