Aside from the tacky custom printed T-Shirts, you can get various items of clothing like hoodies, T-shirts and jackets that you pick out yourself and then send to a company to be printed on, usually this will cost a lot more money than picking one of their own clothing items and also their own designs; it will be something you love, that you can add your stamp to.
Though generally you will have to pick from a series of clothing items they have in stock and pick from the designs they have available, though some do allow you to add your own images and text, like Vista Print. There are other companies out there like Teespring who cater for Techies and funny quotes and images, as well a whole host of other categories; you will have a wide range too choose from.
Bear in mind that the costs vary from site to site, and also from design; they also have campaigns where they have an idea for something to print, but it won’t get printed unless enough people show interest in the campaign and request to get one or more of that item from the campaign.
Whatever you decide to pick, find something that shows the funnier side of who you are.