[kls]

I would second this one, but I would just let the HR guy know they are a friend of a friend and you cannot vouch for them. No more no less. You are helping, you are getting to the right person but you are not putting your name on the line, they cannot ask for more than that.

Networks exist to help one another out, while friends may not be as discerning in their selection they do share a common bond of a mutual friend. You may one day call on your network for help whether it be work or personal life related and I assume you would be pleased if a person in your distant network gave you the opportunity to stand on your own in front of the decision maker. That little advantage can at some times make the difference. But still you are standing on your own accord asking them to extend their credibility without intimately knowing you would be wrong on their part so your should not be expected to do it in your instance.

Now if they have over the top personality flaws like being overbearing, I personal would not want to even make the connection.

[sumeetjain]

Thanks to everyone for their advice. Upvotes to everyone for taking the time to respond.

I like kls's approach, as it doesn't require me to explain a personal methodology for referring candidates to my HR department (as notaddicted's suggestion would have me do).