What should I wear hmmmm !?

All day tomorrow I'm hanging out with my older brother and his mate (who I like) and were going to watch a film first and then going for some tea (what should i wear) and then he's staying at my house (at night when we get home I want to wear something nice but flirty at the same time (probably going to wear pyjamas but what?)) Ive known Gareth (my bros mate) for about 3 years and we always hang out but I think he likes me so I want to make a lasting impression but not a slutty impression! HELP PLEASE xxx:')