It is not offensive nor is it risque. Personally, I feel as if padded bras should be outlawed. I actually find it humorous when Women wear bras that are padded to the max and "push up" or whatever... Like they are fooling someone. First of all, Men really don't care how "large" your breasts really are and secondly, padded bras are noticeable from a mile away. The funniest excuse I hear girls say for wearing them is " It makes my clothes look better". HeeHee. NO... It doesn't. It looks like you have a small chest and are trying to make it look larger so you are purchasing the most padded bras you can find. Sorry. I'm getting a little of track. Back to the question.
NO. It is not offensive nor does it look "trashy" or "slutty". Quite the contrary. It looks like you have breasts (duh. You are female) and don't feel like putting pads over your boobs to make them look deceiving.
Most Helpful Girl
Why would anyone be offended? I don't think "offended" is the word you should have used for this question. If I saw a woman's nipples poking through her shirt I wouldn't feel insulted or "offended". I'd just think to myself, "Maybe she should've worn a bra" and then move on to something else. It's seriously not that big of a deal. It's a nipple through a shirt. It's not like your whole boob popped out of your shirt.
Be yourself do what is comfortable for yourself. If wearing a bra is comfortable for you wear it. If you dislike bras then do not wear it as for nipples poking through no big deal most people are to busy texting while walking to notice.