Does the "bloody nose" trope necessarily imply a sexual situation? If you've seen much anime, you're familiar with the male character getting a bloody nose when he gets sexually excited. For example:




Master Roshi (Dragon Ball) and Umino Iruka (Naruto)

However, when I mentioned this to a Japanese person (someone who was not a big anime viewer), she was confused, and adamant that a bloody nose would normally just mean that the person was excited in general, and it would not necessarily have anything to do with sexual excitement.

This could (and seems likely to be) true for Japanese day to day real life, but very different in anime, where the connection to libido seems very clear.  

Is there someone that can explain this difference? Is the "bloody nose" in anime just used to signify excitement, and it just happens to often (always) be sexual excitement because of the plot? Or is it supposed to be just understood how a bloody nose is interpreted in anime is different from normal life?
Gilles Portras, author of The Anime Companion, wondered the same thing: 


  "So I asked a few Japanese and got a variety of pseudoscientific, and occasionally embarassed, explanations about humidity and blood pressure. But the best response I got was from one fellow who simply recounted that when he was a child he was told by his mother that if he stared at a pretty woman he would get a bloody nose."


It's basically superstition, like if you sneeze once someone is saying something good about you. If you sneeze twice they are saying something bad. If you sneeze three times, you have a cold.