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My basic question is, when people search for tees or clothing meant for their gender, what term do they use...
men's
mens
men
women's
womens
women
In most of my keywords and META tags I am able to use all of them... but for shorter phrases meant to draw in searches, which one would be the best to choose?
Would a crawl bot or search engine decipher between men's and mens in a way that would affect traffic?
well really what I do is I get my teenage friends (im 16) and I have them do searches and based on what they use I use that for clients websites for SEO now on some clients teenagers arent there marketed audience so I would use there marketed audience and have them do a search relating to the service/product and take it from there
Keep in mind that there is more to it then just asking what terms are searched for. What you want are relevant terms that people search for. For example, I have a friend that sells high performance cooling fans for race cars. He could look at the term "Fans" ... for which there are a bazillion searches. Only a very small fraction of those people are looking for his type of fan. Also, there's a bazillion results if you search for that term. So if you were to optimize for that term you would be competing against a very large number of sites. Broad term + high competition = poor results. Instead always try to pick terms which are narrower - "automotive fan" or "High performance Radiator Fan" in the case above for example. The # of searches per month goes down, but those searchers are definitely looking for your product and your sales conversion rate will be much higher. You'll also find that there is much less competition so its easier to get higher rankings. In a nutshell, your terms should be at least 2 words, maybe as many as 4. I look for 200+ searches a month on Google as a minimum, with 1,000+ ideal. Anything over 50,000 month gets tough and over 150,000 is almost certainly too broad or high positioning is not realistically attainable.
Just type in the word and it will show monthly traffic, according to google, Men's and Mens pull in the same average traffic.
I use this all the time. Also listen to the infinity dude above me. You need to go after keywords you can get to the front page of google with if there are too many sites trying for that keyword it won't help you at all.
what do people search for? SEO help... 
