Tony -

You ate ice cream all day and tried to persuade Tony to fill up his swimming pool with ice cream for you to swim in

Steve -

You go to the beach and drool over Steve's perfect body with no shirt on and watch other guys being envious of him

Clint -

You have a water fight and you end up soaked because Clint has perfect aim and yours wasn't as perfect

Bruce -

You sleep in your underwear to try and cool off 

Thor -

You take Thor to a fireworks show at the end of summer when the nights are darker 

Loki -

You take him to a water park and have fun pushing him in the water all day