So many great examples over the years I hardly know where to begin! Guess I'll start at the first one, several years ago. I may have shared this before, sorry if its a repeat but it fits the thread.
We were on a ski trip with a great friend of ours, the three of us have always been very close (and I've known since college he has been attracted to my wife, who is very hot). The friend was trapped in a cold sexless marriage and hadn't had sex in months. I took my wife aside mid-way through the trip and told her about his predicament, and suggested she "help him out" with a blowjob. She had never done anything outside our marriage before and was pretty shocked when I suggested it, but to my amazement she just laughed and turned away shyly, but I noted that she didn't say no.
On the last night of our trip the three of us were out at a bar and the drinks were flowing. She had on a buttondown shirt with no bra underneath. She has medium B cup tits, but very dark nipples and the shirt would gap occasionally giving a nice view of her tits. As the drinking continued, we began teasing her and daring her to unbutton her shirt and show more, which she happily agreed to! By the end of the night she was on the dance floor with the shirt unbuttoned down to her waist, totally flashing the band and our friend. His eyes were just about out of his head and he stared unashamedly right at her tits. She was buzzed pretty good and was loving the attention.
We stumbled back to the condo and I took her to our room while our buddy went to his room to get ready for bed. I took her shirt off so she was topless in her tight jeans. She asked me for help removing her necklace cuz she couldn't unhook the tiny hasp in her condition. I messed with it a little but rather than unhook it I saw my opportunity. I yelled down to our buddy and told him we needed some help in our bedroom. He came walking in to our room and saw her standing there facing him with her tits completely exposed. He helped her get the necklace off, laughing awkwardly but never taking his eyes off her tits. Once the necklace was off I said "well we might as well get her to bed". So we laid her back on the bed, I unbuttoned her pants and together we peeled them off, panties included, so her pussy was also exposed to him.
At this point I knew I had started something but had no idea what would happen next. I didn't need to think about it for long - she sat straight up on the edge of the bed and reached for his pants. She had his pants unbuttoned and his cock out before I knew what was happening! I couldn't believe it, I was in shock as she took his cock straight into her mouth and started sucking him for all she was worth.
He moved to the bed and laid on his back as she went to town on him. He had whiskey dick and has natural stamina anyway (we would find out many times later), so she sucked him for a long time. The whole time her ass was facing me, and I was so hard I started fucking her from behind. It didn't take me long to pump my load into her I was so turned on watching them.
After sucking him for awhile, he got up, turned her around and stuck his cock in her pussy too! I was really shocked again, and thought "wait a sec I didn't say you were allowed to fuck her!". But of course it was already too late
so I just stood back and watched him pound her from behind. He fucked her awhile then pulled out and got in front of her. She took his cock in her mouth and swallowed every drop of his cum. We all passed out on the bed til the next morning.
We've had many sessions with him after that, but that was the first and she was definitely acting in a way described by this thread! There's nothing quite like it when she gets super turned on and takes matters into her own hands (literally), at that point I'm just along for the ride.