Phthalates. Try and say that three times fast! (Actually, it's not that bad - the 'ph' is silent.) "A little plastic each day can keep the testosterone away." That should be our motto when it comes to phthalates: they are just plain dangerous.
Phthalates are not the nastiest chemical in our environment, but they are everywhere. They are added in large quantities in most plastic products you buy and are used in hundreds of agricultural, commercial, residential and consumer products. They are in shampoos, pesticides, soaps, nail polish, lotions, cosmetics, vinyl and fragranced detergents. Even worse, they are used as the coating of some pills and supplements and in air fresheners sprayed throughout homes and businesses.
What's a few phthalates amoung friends? Well, if you're a male, it's bad news: phthalates are nasty xenoestrogens now associated with a host of ills. Hardly a month goes by now without some new study showing the negative effects of phthalates on both us and the environment.
Phthalates are particularly damaging to children. If you have kids or know anyone with children, I hope you'll encourage them to only use glass and stainless steel for cooking. (Also I urge you to keep your use of canned products to an absolute minimum around any boy pre-puberty. See this link on Bisphenol-A for more details.)
What is so tragic is that scientists have known for 30+ years of the dangers of phthalates, yet no one has done anything about it. One 1982 study for example showed that phthalates shunted testosterone-boosting zinc away from the testes.  A study a few years later verifed this and noted actual testicular atrophy (shrinkage). 
Lest you think I am exagerrating, let me point out just a few of the studies showing problems with phthalates:
1. Effeminization. A recent study demonstrated that the higher the levels of phlthates in the mother's urine, the less likely their boys were to play with regular male toys, i.e. they appeared to be effeminized.  Extra estrogens during these critical years can permanently alter the young male brain. Animal studies clearly show that phthalate exposure can alter SHBG, testosterone and LH (leutinizing hormone) levels. 
2. Testosterone. These are potent endocrine disruptors that every hormone-luvin' male should avoid like the plague. One study examined dosages of 100, 80, 60, 40, 20, 10, 5, or 0% of the mixture.on fetal rates and found a dose-dependent decrease in testosterone, meaning the more phthalates, the less the testosterone.  Needless to say, this is very, very bad for males in the fetus or young children.
3. Fertility. Further proof of phthalates' gonad-killing properties are linked to lowered sperm quality  and DNA damage . See my link on Male Fertility for additional information.
4. ADHD. The decreased testosterone and other attributes of phthalates actually alter the male brain and one study showed a link to ADHD.  For more information, see my link on Environmental Causes of ADHD.
Did you know you can inexpensively do your own testing for most hormones? The industry leader is Discounted Labs..
5. Thyroid. Many studies have verified that phthalates alter thyroid function. This is particularly dangerous for the little ones and one study warned "even small changes in thyroid homeostasis may adversely affect human health, and especially fetal neurological development may be vulnerable." 
6. Insulin Resistance and Diabetes. These chemicals seem to wreak havoc with the body's blood glucose systems and have been implicated in several studies (on both men and women) as a contributor to insulin resistance, metabolic disorder, prediabetes and diabetes.  The reason? Testosterone, as I document in my book Low Testosterone by the Numbers, regulates insulin sensitivity in men.
This list could go on and on. Again, one should be as cautious as one's budget will allow, buying organic - many pesticides are phthalates - and using only stainless steel/glass for cooking and natural means for pest control.
2) International Journal of Andrology, 29(1):172-180, Published Online 7 Feb 2006, "Possible impact of phthalates on infant reproductive health"
3) Toxicological Sciences, 2008, 105(1):153-165, "A Mixture of Five Phthalate Esters Inhibits Fetal Testicular Testosterone Production in the Sprague-Dawley Rat in a Cum7) J Appl Toxicol, 1989 Aug, 9(4):277-83, "Mechanism of testicular atrophy induced by di-n-butyl phthalate in rats". Part 1.
4) Toxicological Sciences, 2008, 105(1):153-165, "A Mixture of Five Phthalate Esters Inhibits Fetal Testicular Testosterone Production in the Sprague-Dawley Rat in a Cumulative, Dose-Additive Manner"
5) Environ Health Perspect, 2003, 111:1164-1169, "The Relationship between Environmental Exposures to Phthalates and DNA Damage in Human Sperm Using the Neutral Comet Assay"
6) Human Reproduction, 19(5):1121-1126."Demonstration of Chlamydia trachomatis IgG antibodies in the male partner of the infertile couple is correlated with a reduced likelihood of achieving pregnancy"
8) Biological Psychiatry, 15 Nov 15 2009, 66(10):958-963, "Phthalates Exposure and Attention-Deficit/Hyperactivity Disorder in School-Age Children"
9) European Journal of Endocrinology, 2006, 154(5):599-611, "Environmental chemicals and thyroid function"
11) Environ Health Perspect, 2007 June, 115(6): 876 882, "Concentrations of Urinary Phthalate Metabolites Are Associated with Increased Waist Circumference and Insulin Resistance in Adult U.S. Males"