So i am a tall guy 6'4" but also pretty slim(about 195-200lbs). I buy all my dress shirts in a slim fit so that they dont balloon on me because i have to buy pretty large shirts to fit my arm length. but because of this, they tend to run a little short in the waist.
I always have issues with my shirts coming untucked in the back, especially when i am sitting at my desk. So i went out and bout a pack of hanes undershirts in a Tall size. when i opened the package i was surprised to find they were actaully like legit tall tees.
anyways, they tuck in sooooo much better than normal undershirts, and they keep my dress shirts tucked in perfectly as well. so for all you tall guys with this issue, buy some tall tees and you will be soooo much more comfy.
The first time that i ever wore a tall tee was to work, and i will never wear normal undershirts again if i can help it.