Or squish him or her tightly against you? Don't worry. You are more than likely a sane adult who functions well in society. According to Rebecca Dyer and Oriana Aragon, two Yale University psychologists, "some things are just so cute, we can't even handle it." From Scientific American:
Cute aggression's prevalence does not mean that people actually want to harm cuddly critters, Aragon explains. Rather the response could be protective, or it could be the brain's way of tamping down or venting extreme feelings of giddiness and happiness. The scientists are currently conducting additional studies to determine what drives the need to squeeze.