Uber driver here. I have had passengers ask me for dates, which I either politely declined, or hinted what bars I go to and implied that if they came across me in a more appropriate setting while they were still sober (my passengers are generally intoxicated) they were welcome to re-introduce themselves and say hello. If I feel tempted to hold the passenger at gunpoint and order them out of the car, this negatively impacts their rating, and could cause them to lose access to the service. Generally, this behavior includes touching me. Don't fucking touch me. And be careful with your stun gun or cattle prod that you pull out for your walk to your building because, as one of my passengers almost found out, if it goes off in my car I will assume I'm being attacked and I'm ready and willing to open fire. In my case, I'm a woman, alone at night, locked in my car with strangers.
Having said that, there have been some fairly aggressive, but politely worded sexual propositions. These were all declined, but because I wasn't disrespected, it had no negative impact on their rating. Make no mistake though, I see myself as a cabbie, a designated driver, a patron saint of the drunk, stoned, and stupid, not a prostitute. I'm not granting sexual favors to strangers in my car. I still have other ride shares to do, and my family to transport the next day. Even a passenger who seriously inconveniences me or deeply offends me can still get five stars if they tip at least $5 and promise to give me 5 stars.
In conclusion: If you want to suck his dick, find a charming way to offer. If he takes offense, apologize, then at the end, give him $5+ and 5 stars. Best case, you get to suck his dick. Worst case you get matched for a ride share again with someone who thinks you're grimy, and remembers why.