The 70's era in fashion can be best exemplified by disco. Movie starts during this era, like John Travolta, helped bring platform shoes, three pieced suits and tight bell bottomed jeans into popularity in the 70's. Therefore, bringing the mentioned pieces into one ensemble can help create a 70's costume for men.
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Creating a 70's costume for men.
Hairstyle for men in the 70s were characterized by the afro, mullet and the shag cut. Pick one of the characteristic styles of the 70's that appeals to you. Any of the three will help define your 1970's costume.
Pick a three piece suit of any color that particularly have wide lapels and high rise vests. Colorful three-piece suits became very popular in the 70's, so the louder the color, the better!
Flared trousers or bell bottoms were particular iconic in the 1970s, pick a pair of a nice pair of flared jeans. Flared jeans hug tight to the thighs and flare out to the bottom where your foot is. If you do not have a pair of flared jeans, you can create the bell bottomed look by cutting in the outer seams of a regular pair of jeans.
Pair your outfit with platform shoes. Platform shoes should be available at costume stores or even on ebay (or other online sites).