Thinking about Benign Violation Theory it is interesting to think about whether the act of laughing is itself funny. I think it is. We know that it's behaviourally contagious which means that if you see someone laughing you're likely to do it yourself, but is there an element of humour to a laugh?
Of course there is. The act of laughing is entirely a violation, it's not something that someone would normally do, it usually serves no purpose in the situation, in fact it incapacitates a person in the most ridiculous way, causing them to lose control of all sorts of their normal bodily functions. The fact that we recognise it at laughter means we know it's not actually dangerous to the person (or a threat to ourselves, which unexpected behaviour could always be) and therefore it fits the criteria perfectly.
The fact that laughter is a response to something funny means that there's also likely to be a truly funny thing in close proximity so there is the added frisson that maybe you will soon experience that funny thing too. The feeling of seeing someone laugh and being all like, "What? What is it?" because you want in on the joke is a familiar one.
The anticipation of laughter is just as good for us as laughter itself so that's all to the good.