Oh yeah. My forearms all the time...be out drinking with friends, speaking in an animated way, and bash my arms off the table (a lot harder than I noticed at the time of doing it). Wake up the next day and wonder how it happened, it didn't seem like I had hit my arms too hard. All the time for the last year and a half maybe.
A few other ones from walking into stuff too, though those were a bit less common at least.