Spotted...

It's really easy--just ask yourself what would be correct:

'making offensive gestures at sumo' -- correct (obviously--no problem with a name)
'making offensive gestures at I' -- obviously not correct
'making offensive gestures at me' -- correct

Hence:

'making offensive gestures at sumo and me'

Just do that test quickly every time--separate out the different components in the list and then put them together. E.g., suppose you're with a female friend as well as sumo:

'making offensive gestures at sumo, her, and me'

'making offensive gestures at she' would be wrong, hence 'her'.

However, in another case:

'sumo, she and I were making offensive gestures at spotter.'

It's not:

'sumo, her, and me were making offensive gestures at spotter.'

Do the check--you can't say:

'Her was making offensive gestures at spotter.'

or

'Me was making offensive gestures at spotter.'

It's easy to find out just by asking yourself this pattern of quick question every time.