A person, usually a friend who is a burden in a social situation. They may even slope away and hover a couple a metres away whilst you talk to someone they don't know. Also could be described as a high maintenance friend you have to look after in any social situation or occasion.
Clive is such a social burden. I was talking to Jeffrey and tried to introduce Clive, but he just looked awkward and moved a few metres away and put me under pressure to finish my conversation. It's like babysitting when you go on a night out with Clive.