Never again

a week ago I let my buddy borrow my civic to go pick up his girl. I was hesitant about lending it out but I trusted him and he offered to fill up the tank. Got the car back and it fine. Well today I went to fill up and the gas cap was missing. So I've been driving around with no compression in the tank for a week. Will this cause any problems for me or is it not a big deal? I have a new cap on order but i'm still worried about the past week.

Seen the same thing on a mates Celica, did nothing other than spew fuel from the uncovered outlet when he took a hard corner!!!:p

almost didnt pass smog cause i ran mine over ... dont ask ... had to get a new one.