No really, what's cuter then a baby sucking its thumb?
When I was washing off constantly dropped pacis with B, I dreamt how nice it would be to have a thumb sucker! Then a friends little girl wouldn't stop sucking hers, so I thought meh, maybe it's ok. So R has been our first thumb sucker but it just tickles my bones!! First from obvious cuteness, and then for him to be able to soothe his need to suck without mama sometimes, and then third, I've been told its good for their brains...i love it. Thumb sucking also re-optimizes heart rate and can help a baby digest more efficiently.
But no, it's not cute when adult do it, so you might want to stick to aromatherapy or music to calm you down ;)