If i had a foot fetish would i be required to stare at the ceiling so that the object of my fetish doesn't end up on my eye line? Maybe.
But it would be an easier conversation starter at the gym ... "damn dude you have huge feet!" Altho, the minute you say it, the obvious double entendre is to be expected... "You know what they say about big feet..."
Consider 2 guys who are more closely associated by age, peer group, etc. It may be easier to tease and ball bust over big feet in the locker changing area, since the showers can have noise and echos... not always conducive to conversation.
Ultimately it depends on how well guys know each other. In a locker room, If you are yourself open and friendly its usually possible to strike up an easygoing chat with a stranger nearby. People like to talk about themselves (how long have you been lifting?") And they like to be flattered "(Cool Nikes!" ) . Some may like to make friends (I see you hear alot at this time- can i get you to spot me something?)
At a bar you again have to start slow and gain trust and an even level of exchange- then you can risk insults shared in humor - " Dude you look like you slept in your clothes!" But you work your way up to the edgy, sexual or possibly insulting comments. Its like in fishing - you have to set the hook before you start reeling, otherwise you will lose the catch.
Once you have a comfortable and trustworthy rapport, a friend can get away with saying and doing a lot more because the meaning is understood.