How old is he? This is regurgitation behavior (in all liklihood) but you do NOT want to encourage it. If this is an an adult bird, this is a sexual behavior and often means that certain environmental factors make it more likely to occur. It could be vomiting, but that is usually less controlled and less specific to one person's presence etc.
As humans, we often inadvertently sexually stimulate birds (providing shadowy spaces, boxes, tents etc= not good). Pet on the head and neck only and also ensure that your parrot gets a bare minimum of 10 solid hours sleep per-night. You don't want your bird to see you as its mate (as this is how they feed their mates). I am not saying it will never happen (even with the best of hormonal controls), but it's not something you want to encourage...Even though it is a compliment, it can get complicated very quickly when they see you as their mate and other factors are not controlled.