I'm so glad you referenced this matter! It is at the heart of my own recent (past year or so) musings about the nature of sexual interaction. To restate the position taken by Tomkins, shame affect is triggered only in those situations characterized by an ongoing source of interest-excitement or enjoyment-joy (one that is not turned off during the events to be described). Now something happens: an internal or external event, a thought, another source of affect. Shame affect is the amplified analogue of that interference with the ability of the preexisting trigger to produce and maintain positive affect. Shame affect not only occurs in reaction to the impediment, but as an amplified analogue of that impediment, causing much more impediment than occurred before it was triggered. When I lecture on affect theory these days, I use the image of a bank of nine spotlights, each a different color, turned on by a different switch, each color motivating us to act differently on whatever triggering source it then illuminates. I then characterize the spotlight for shame as a "darkness beam," something that obscures whatever it "illuminates."
My favorite example of an impediment is what happens when lovers are communing by the mutualization of smiles and laughter; for a moment, one of them does not "get" the joke, or is drawn into an association that has nothing to do with the partner. The tiniest of alterations in the display of positive affect on the face of the one who has been distracted will now act as an impediment to the continuation of this positive affect in the other. This produces shame (recall all the instances of this in your own life---it feels really awful when this happens) that is not relieved until communicated to the partner who had been distracted, and who then reconfirms the existence of mutualized positive affect; it is this reconfirmation that turns off the shame and allows positive affect to reign again. This, then, is an example of positive affect interrupted in a situation where there is plenty of reason for that affect to continue; shame is the response to the temporary interruption in that ongoing positive affect. Tomkins said often that people with chronic shame are the most loving of all because they walk around with the sturdy belief that happiness lurks just around the corner.
Surprisingly, this is the area where my good friend and colleague Francis (Frank) Broucek gets stuck. Frank cites the example of someone who is watching the television set with evident interest; all at once the electricity goes off. We know that a dead television set cannot produce images, and there is no reason for continued interest-excitement in whatever is on the screen. Frank says that this is the type of reduction in positive affect that fits SST's criteria for the triggering of shame, and that surely there is no shame here. He's right that there is no shame in the television scenario just quoted, but wrong to say that this example invalidates SST's model for shame, and that shame is an inherently social emotion. I remain fascinated by the number of people who insist that shame can only be defined in an interpersonal context. Even though my example of lovers is of course interpersonal, you can observe infants and small children turn away with characteristic shame reactions while they are experiencing momentary failure at some private task.
But back to sex: One of the reasons I devoted so much space to a new theory of sexuality in "Shame and Pride" is that Freud declared that there was an obligatory connection between shame and sexuality, and that in order to maintain the strict separation between drive and affect postulated by Tomkins, I had to show how sex and shame became coupled. I suggested that the onrush of arousal occurs at exactly the rising gradient necessary to trigger interest-excitement; that a faster rate of rise would have triggered fear-terror, a much much slower rate of rise triggered no affect, and a steady-state experience of arousal triggered distress-anguish or anger-rage. So sexual arousal is the quintessential example of a rising gradient that triggers interest-excitement. As children and adolescents, sexual arousal rarely leads to sexual satisfaction---until we actually get connected to others for sexual experience, nearly all of our arousal-excitement experiences are impeded by the reality of disinterest on the part of everybody else. Merely to be aroused (get dripping wet, spring a boner, etc.) is a major source of shame for every hot young person.
So how do we ever get to be sexual with another person? Only by learning that moderate episodes of shame affect occuring during necking, petting, etc. (because no partner can read our minds adequately to allow us avoidance of momentary feelings of misconnection that is an impediment) can be undone by increasing the degree of our excitement and arousal. Here is a perfect example of the way normative bouts of shame may be overcome---sequential increases in interest-excitement that mutualize within the couple and lead to increased arousal and eventually mutual permission for intercourse (an activity during which most people close their eyes in order to limit the degree to which the partner's gestures may be taken as an impediment, a trigger to shame, and the cause of a consequent loss of arousal.)
I believe that this sequence is very important in the nature of interpersonal sexuality, and that it is based on the relation between shame as triggered by an impediment to interest-excitement and our ability to increase positive affect in order to overcome the impediment. Incidentally, and not too terribly off the topic, this is why I believe cocaine and the amphetamines are popular. I think they allow someone who has been frozen by chronic shame to experience artificially enhanced interest-excitement and possibly something that feels like good sex.