As a host (and as a guest) to a gaming session, I like to help make the experience as gratifying for as many people as possible. I sometimes run into certain types of people or behaviors that are sometimes, but never always, anticipated.
Sore Loser Crankiness: gets increasingly irritable as the certainty of his failure to win approaches.
Self-Pitying: repeatedly moping sadly and verbally over how desperate, pathetic and impossible his situation is.
Vendetta-bound: out for blood beyond any intra- or inter-meta-game statistics or standing reason. Spouses, Significant others, Politically mis-aligned players, someone who took the last pizza roll.
There are more, and I listed these as behaviors, not so much as 'types of people', although we probably all know various people who tend to repeatedly show these behaviors. Some might be "tolerate" and others might be "kick to the curb", but do people have good approaches that help address these issues and in the end make their gaming sessions and gaming groups stronger?
I'd also like to add that I'm more interested in courses of action during the ongoing game session or social event (excluding something like pulling the person aside for a word). I feel there are various common carefully thought out ways to confront or appeal to people after the fact and that these approaches (in person, calling, email, tone of appeal/confrontation) could easily be another question/topic.
I've edited the original question to specify adults as interacting with children adds in a whole extra complexity of boundaries especially when they aren't your children and you're then thinking about how to interact around or with the parents.