Early 80's Girlfriends pantyhose

Just to give you an insight.....

When I was s1xte6n I used to meet my then Girlfriend who was f1fte5n from her school, she used to wear a blue tartan knee-length wrap around skirt with sheer navy blue tights.

We went upstairs on the old route master bus and sat down at the back, there was only 1 other passenger, a middle aged man reading a book.
She sat with her leg crossed over and her ankle was on top of her knee so I could see up her skirt. That little white triangle of her panties through her sheer tights was cock hardening. I was stroking her inside leg and going higher.
I noticed her skirt was open at the join and was showing her legs. The middle aged man was looking now while I was kissing my GF.
I kept stroking her legs and saw the mans arm start to move up and down quicker, he was wanking looking at my GF's nylon clad legs.I parted her legs wider. He didn't know I saw him.
I kept kissing her and saw his cum shoot out over the seat, he got up red in the face and hurried downstairs.

I'd love to know if anyone else has had an experience like this.