COMMUNICATE both verbal and non verbal and a good time will be had by all involved!!!

I'd like to reinforce what LB is saying here:  Good sex requires communication, even if he's your BF/partner and you've done it together a thousand times.  Although I like porn (don't we all, or we wouldn't be here!), I think it's unreal to have guys screwing away with no communication about what they like/want/don't like/don't want/etc.

As a top for the last ten years who started out as a bottom, I think the guys you meet who have loose, floppy arses that don't stimulate your cock are probably trying too hard to relax–they've mastered that [relaxation] technique very well, and just need to be asked to clamp down a bit.  After all, they are able to tighten up when avoiding a bowel movement!

For guys who are "too tight" and in pain, they're on the other side of this situation:  They need to learn to relax their sphincter.  But this is not intuitive for many guys–relaxing the sphincter is usually associated with taking a shit, and that's not something a guy--especially a novice--wants to do in the middle of sex.  But if he's empty and clean inside (which we hope is the case), nothing will come out.  I remember one college guy who had so much trouble relaxing this way that I led him into the bathroom, had him sit down on the loo, and try to shit.  When he saw that nothing would come out regardless of how much he relaxed and even pushed, he was more confident about relaxing in bed and we had a great time.

A final note:  One time I hooked up with a bottom who had a genuinely small arsehole.  He relaxed completely, enjoyed immensely getting fucked, but it was so tight around my cock that I'm the one who was in mild pain--I kept putting on more lube, but it was still too tight.  I was happy when he finally came so I could pull out, and then he finished me off with his mouth.  But this guy is the exception rather than the rule, and no, I don't still have his phone number 

have i said too much? lol

Jagged, Thank you for your reply. nothing is too much In fact I want more..  :hug2:

Dear leatherbear,
Thank you for your advices, especially on the communication and the "smack his a**" part

I met a size-queen bottom guy, he likes to get f* by a big hard one, When we did anal x, The first penetration is good. However subsequently, I almost feel nothing. = This result in, I could not cum.

In my opinion this is a bottom that has been overly used or is inexperienced. Smack his ass hard and if he tightens up then you will know that it can be tighter and let him know this is what you like. However, if it does not tighten up pull out and use your fist    or wash up and finish orally instead. Some Bottoms do not understand the idea of too loose is no fun for the top. Being a Top is so much more than who is on top. A good Top will take control of the situation and educate the bottom to His needs and also make sure the bottom is satisfied as well.So, be more vocal during sex and see if this changes the results of the event.

I met a less frequent bottom guy, he rarely takes cock inside him. What i did was to make him relax (lick, rim, fingering, etc…). After he is relax, I will start the action. The catch is, when the bottom feel pain = it is good feeling for me.
However I feel bad about the bottom feeling pain for my pleasure 

I do not think very many men would be in "real pain" and not bring things to a halt.There is,however, always the possibility that you met a true "Masochist" and then you should have pumped harder .(BTW: I want his phone # as well.) Seriously, communication will resolve this issue  also.

Is the scenario that i mentioned is due to the reason that i have not meet with a good bottom? Or Do you experiences the same scenario as i did?

Good Bottoms are made by Good Tops and as always communication is the "key" to better sex.

Is there any other experiences that I have not mentioned (like the gym bottom guy, who work out his back. mmm )?

Who does not like a "gym bottom guy" ? But that will not necessarily make him tighter. However, we are talking about sphincter muscles after all and they can be "worked out" like any other muscle.( please refer to "smack that ass" above )
You can even use "gym" equipment to have sex on but body muscles do not make for a tight ass. That takes another kind of "exercise" that does not require a gym or any equipment at all.

What do you do to satisfy your sex-partner at the same time satisfy yourself?

COMMUNICATE both verbal and non verbal and a good time will be had by all involved!!!

as for the pain
some pain is pleasurable
i guess the bottom will always say if he's had enough
or if it hurts too much
it's important then for the top to listen and respect the bottom's feelings
but if he's moaning and groaning but not trying to stop you
then i guess you can keep pumping away lol

i always hate sex if the partner is just treated like an object
i think it's always important to remember your partner is a person
and no matter how weird the sex act is
each other's dignity ought always to be respected

have i said too much? lol