When I talk to girls I shut down and stammer not knowing what to say. I feel like the whole room is staring at me expecting a witty remark and I can't deliver. How do I get out of my head and into the game?

(For the record I am asking as an endorsed contributor who does not have this issue; I am asking because I am thinking about how I would advise an RP newbie and wanted to bounce this off the community. Let's say the asker is 20yo white male college STEM undergrad height/weight proportionate who works out but not too seriously.)

EDIT: Just to clarify, I am asking advice about giving advice.