...I'd say the following.
Leonard: Forget about Penny and find a nice girl who actually appreciates the same things you do.
Amy: Dump Sheldon. He doesn't care about you as more than a friend beyond some possessive inclinations. Assume an aromantic friendly relationship based on intellectual stimulation. And then ask her out.
Raj: Even if he wasn't straight, Howard's in a committed relationship with Bernadette, so stop making him feel uncomfortable with your obvious attraction to him.
Penny: You don't have to change your whole identity for a guy, but it wouldn't kill you to be a bit more respectful either.
Jeez, these people are dysfunctional!