I made a halter top out of a plain white men's t-shirt today. It was the easiest project I've ever done, and it literally took one minute.
To make one yourself:
1. Use any cotton t-shirt.
2. Cut off one of the sleeves.
3. Starting at the top of the t-shirt collar on the same side where you cut off the sleeve, cut diagonally down across the shirt to right underneath the armpit of the other sleeve. It now should look like a one-shouldered tank top.
4. Spin the shirt around so the cut sleeve is facing you. The sleeve opening is the part of the halter that loops around your neck, and the wider diagonal cut has now become the open back of the shirt.
5. Embellish or tailor as you wish. I prefer to leave the halter top unaltered and loose... it gives it a careless, casual vibe.
You can wear this halter to the beach, or tuck it into a skirt or pair of pants for a cute party look. Try making a mini dress by using an XXL t-shirt.