here's your luck ms. FerminaDaza
well, its not a really nice thing to say to a guy that he has a small thingy. like you said, it will just add to his insecurity.
but a lot of guys are always insecure about their thingy, thinking that its small or the size is not enough. probably because we guys would tend to compare it to those that we see on porn movies and such.
like myself, ive been insecure before of my size but those whom ive had sex with would always be back for more (sorry may halong yabang), and when i read in a lot of forums that the average is 5 inches, then thats when my insecurity faded.
going back to the question, if you tell your guy that he has a small thing, its like laughing at the disability of a disabled individual.
hope this helps