Well that escalated quickly 🙃

Just to make it clearer here's a pic.

The most sensitive place on a penis is the Frenulum, just under the V of the underside of the head.

If a guy hasn't ejaculated for a while the stimulation of just this spot with a tongue or finger can be enough to get him off.

When obtaining manual release I enjoy the thumb hitting this spot as the shaft is stroked as well as when actually tossing off.

Stimulation of this area when soft brings on a fast erection too.

In the interests of scientific research for you I've just browsed some of my favourite posts....

The first thing I guess about a growing erection is feeling a slight pressure building - so if I'm wearing jeans or tighter pants I'll feel the gradually growing bulge increase in size and press both against my clothes and against my body. With it is a feeling of warmth. Not to the same extent or speed as a wetting yourself spurt warmth, but just a gentle comfortable glow like maybe gripping one of those hand warmer pads.

Depending on clothing, as my penis gets more erect it can be a touch uncomfortable until I adjust its position. Normally the soft penis can be a bit curled up especially when clothed and of course the erection wants it to stand straight - which sometimes needs a bit of adjustment.

As well as the warmth and the feeling of swelling, there's also a comforting sort of faint tingle too - which could be in my mind more than physical. The other thing that's a little hard to describe are the changes in feeling.  Normally my balls and that spot inside each thigh are very ticklish, but as soon as erection sets in they get very sensitive, with any touch working to increase the horniness level. In that way I can almost climax just from gentle touch there alone, without the need for any other stimulations - and as soon as I have done I'm back to ticklish as hell.

Moving onto my shaft, the erection and the horniness with it just begs for my penis to be held, like some sort of magnetic attraction. The erection is caused of course by blood flow and pressure within the penis, and feeling the grip of a hand around it, or better still a warm cervix adds to the pressure and heightens the feeling too.

I'm one of those European types who aren't circumcised as standard and hence whilst all this is going on my normally baggy foreskin has been pulled tight, with the tip of my penis poking out. Taking the erection to the maximum (and giving it a helping hand) my foreskin will slip back to behind the ridge of my glans, exposing it to the world.  Probably because it's normally safely covered that can feel amazing - for example during oral or penetration - or if pressing against clothing or rubbed roughly can be quite uncomfortable.

When erect there's a muscle somewhere deep in my pelvic region that I can clench and add an extra little push to the erection - I guess pushing a little extra blood pressure in there. It's a bit like the push you give to start your pee flowing when desperate, although a slightly different muscle.

Talking of starting pee flowing, as you probably already know the body is designed to allow one or the other - in my case if I'm desperate to pee I find it difficult to get a hard on at all until I've taken care of that need.  If I do, it generally takes the erection to at least partly subside before I can force any pee out - and then it's like trying to squeeze out a pee when you don't really need to.  That enlargement and pressure inside the penis also has the effect of changing the urethra shape so I get a more powerful jet, sometimes multiple splattering streams too- generally making more of a mess than usual.

Hopefully that little bit of scienctific research has told you what you need to know - happy to answer any specific questions....