Let's define a selfless act first: To do something without benefit for yourself.
I believe that benefit includes feelings. After all, you are not truly selfless if you feel that what you are doing is right and it makes you feel good. You have other motivations. Helping the other person is a side effect of making yourself feel good. People don't give money because they're selfless. People give money because they feel it is the right thing to do, and that satisfies their feeling of justice or whatever. Gandhi did what he did because he felt it was the right thing to do. Which must have given him pleasure. If he 'felt' it was wrong what he was doing, but knew it was the right thing to do, he wouldn't have done it, I think.
To give you an example: would you torture your sibling to save a million people? Would go at them with a knife and extend their suffering for as long as humanly possible, if it was the only way to save an entire continent? Would you murder hundreds and forsake yourself and your own self-respect if it meant saving a species? I know very few people who would say yes. And yet, I think that is selflessness. To forsake yourself, and your feeling of self, for the benefit of a thousand. This has come up loads of times in movies: sacrificing one for a million, or a hundred for a billion, is according to the movies, never right. Experimenting on the few for the benefit of the species is amoral and wrong. And yet, from the point of view of the species, is it really?
Is it not truly selfless to let this horror go on because you KNOW it will be for the benefit of the species? Ponder about this for a bit. I dare you. Could you do something you would never do if it meant the survival of everyone you know? That, I believe, is what it means to be selfless. Not giving a homeless man enough money to buy a differently faced coin of the same value.