ie) Someone who merely acts like a friend but has a constant [hidden agenda]. A friend who is [ungenuine] would likely not keep in touch over a period of time only to [hit you up] out of the blue because it turns out they actually need something from you.

[Ungenuine] can also be used to describe someone who treats women with disrespect, fools around with multiple women in a given sitting at a given location (usually an aggressive type), untrustworthy, is overly sensitive about jokes, and is otherwise not a person who the rest of the group is fond of.